diff --git a/api/app-api/build.gradle.kts b/api/app-api/build.gradle.kts
index 73240a99..3c1ca940 100644
--- a/api/app-api/build.gradle.kts
+++ b/api/app-api/build.gradle.kts
@@ -16,6 +16,8 @@ dependencies {
     implementation(platform(libs.springBootDependenciesBom))
     implementation(libs.springBootStarterWebmvc)
     implementation(libs.springBootStarterValidation)
+    implementation(libs.springBootStarterAspectj)
+    implementation(libs.springTx)
     implementation(libs.springdocStarterWebmvcUi)
 
     testImplementation(platform(libs.springBootDependenciesBom))
diff --git a/api/app-api/src/main/java/kr/ac/kookmin/stream/api/app/welfare/rental/AppRentalApi.java b/api/app-api/src/main/java/kr/ac/kookmin/stream/api/app/welfare/rental/AppRentalApi.java
index f5b828c6..2f127966 100644
--- a/api/app-api/src/main/java/kr/ac/kookmin/stream/api/app/welfare/rental/AppRentalApi.java
+++ b/api/app-api/src/main/java/kr/ac/kookmin/stream/api/app/welfare/rental/AppRentalApi.java
@@ -4,6 +4,7 @@
 import io.swagger.v3.oas.annotations.tags.Tag;
 import kr.ac.kookmin.stream.api.app.AppApiUser;
 import kr.ac.kookmin.stream.api.app.welfare.rental.request.ItemListParams;
+import kr.ac.kookmin.stream.api.app.welfare.rental.request.RentalApplyRequest;
 import kr.ac.kookmin.stream.api.app.welfare.rental.request.RentalHistoryListParams;
 import kr.ac.kookmin.stream.api.app.welfare.rental.response.ItemListItemResponse;
 import kr.ac.kookmin.stream.api.app.welfare.rental.response.RentalHistoryListResponse;
@@ -12,6 +13,7 @@
 import kr.ac.kookmin.stream.api.common.dto.CursorSliceResponse;
 import kr.ac.kookmin.stream.api.common.openapi.ApiErrorCode;
 import kr.ac.kookmin.stream.common.CommonErrorCode;
+import kr.ac.kookmin.stream.welfare.domain.fee.domain.FeeErrorCode;
 import kr.ac.kookmin.stream.welfare.domain.rental.domain.RentalErrorCode;
 import org.springdoc.core.annotations.ParameterObject;
 
@@ -46,4 +48,25 @@ ApiResponse<RentalHistoryListResponse> getHistories(
         description = "지금 반납해야 하는 대여(대여 중 상태)와 반납 기한(dueAt)을 조회한다. "
             + "반납 기한은 대여일에 최대 대여 일수를 더한 날의 반납 마감 시각이다. 없으면 빈 배열이다.")
     ApiResponse<ReturnRequiredListResponse> getReturnRequired(AppApiUser apiUser);
+
+    /** 대여 신청. 회비 납부·재고·중복 대여·대여 가능 시간을 검증한 뒤 이력을 만든다. */
+    @Operation(summary = "대여 신청",
+        description = "물품을 대여 신청한다. 대여 시간은 영업시간(10~17시) 안이어야 하고 점심시간(12~13시)은 제외된다. "
+            + "이미 대여 중인 같은 물품이 있으면 거부하되, ignoreDuplicate=true면 건너뛴다. "
+            + "소모품은 신청 즉시 반납 완료로, 대여품은 대여 중으로 등록된다.")
+    @ApiErrorCode(type = CommonErrorCode.class, codes = {"INVALID_INPUT"})
+    @ApiErrorCode(type = FeeErrorCode.class, codes = {"MEMBER_IS_NOT_PAYER"})
+    @ApiErrorCode(
+        type = RentalErrorCode.class,
+        codes = {
+            "ITEM_NOT_FOUND", "ITEM_OUT_OF_STOCK", "RENTAL_ITEM_DUPLICATED",
+            "INVALID_RENTAL_TIME_RANGE", "INVALID_RENTAL_TIME_LUNCH_BREAK"
+        }
+    )
+    ApiResponse<Void> applyRental(AppApiUser apiUser, RentalApplyRequest request);
+
+    /** 반납 신청. 본인 소유의 대여 중 이력만 대상이다. */
+    @Operation(summary = "반납 신청", description = "대여 중인 물품의 반납을 신청한다. 신청 즉시 반납 완료로 처리된다.")
+    @ApiErrorCode(type = RentalErrorCode.class, codes = {"RENTAL_NOT_FOUND"})
+    ApiResponse<Void> returnRental(AppApiUser apiUser, Long rentalHistoryId);
 }
diff --git a/api/app-api/src/main/java/kr/ac/kookmin/stream/api/app/welfare/rental/AppRentalController.java b/api/app-api/src/main/java/kr/ac/kookmin/stream/api/app/welfare/rental/AppRentalController.java
index 974387ba..385feacd 100644
--- a/api/app-api/src/main/java/kr/ac/kookmin/stream/api/app/welfare/rental/AppRentalController.java
+++ b/api/app-api/src/main/java/kr/ac/kookmin/stream/api/app/welfare/rental/AppRentalController.java
@@ -3,19 +3,26 @@
 import jakarta.validation.Valid;
 import kr.ac.kookmin.stream.api.app.AppApiUser;
 import kr.ac.kookmin.stream.api.app.welfare.rental.request.ItemListParams;
+import kr.ac.kookmin.stream.api.app.welfare.rental.request.RentalApplyRequest;
 import kr.ac.kookmin.stream.api.app.welfare.rental.request.RentalHistoryListParams;
 import kr.ac.kookmin.stream.api.app.welfare.rental.response.ItemListItemResponse;
 import kr.ac.kookmin.stream.api.app.welfare.rental.response.RentalHistoryListResponse;
 import kr.ac.kookmin.stream.api.app.welfare.rental.response.ReturnRequiredListResponse;
+import kr.ac.kookmin.stream.api.app.welfare.rental.usecase.RentalApplyUseCase;
 import kr.ac.kookmin.stream.api.common.dto.ApiResponse;
 import kr.ac.kookmin.stream.api.common.dto.CursorSliceResponse;
 import kr.ac.kookmin.stream.common.CursorSliceResult;
 import kr.ac.kookmin.stream.welfare.domain.rental.domain.Item;
 import kr.ac.kookmin.stream.welfare.domain.rental.service.ItemService;
 import kr.ac.kookmin.stream.welfare.domain.rental.service.RentalHistoryService;
+import kr.ac.kookmin.stream.welfare.domain.rental.service.RentalTimeValidator;
 import lombok.RequiredArgsConstructor;
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.ModelAttribute;
+import org.springframework.web.bind.annotation.PatchMapping;
+import org.springframework.web.bind.annotation.PathVariable;
+import org.springframework.web.bind.annotation.PostMapping;
+import org.springframework.web.bind.annotation.RequestBody;
 import org.springframework.web.bind.annotation.RequestMapping;
 import org.springframework.web.bind.annotation.RestController;
 
@@ -26,6 +33,7 @@ public class AppRentalController implements AppRentalApi {
 
     private final ItemService itemService;
     private final RentalHistoryService rentalHistoryService;
+    private final RentalApplyUseCase rentalApplyUseCase;
 
     @Override
     @GetMapping("/items")
@@ -56,4 +64,27 @@ public ApiResponse<ReturnRequiredListResponse> getReturnRequired(AppApiUser apiU
             rentalHistoryService.getReturnRequiredRentals(apiUser.userId())
         ));
     }
+
+    @Override
+    @PostMapping("/histories")
+    public ApiResponse<Void> applyRental(AppApiUser apiUser, @Valid @RequestBody RentalApplyRequest request) {
+        // DB에 안 닿는 순수 검증은 트랜잭션(UseCase) 진입 전에 끝낸다 — 잘못된 요청이 커넥션을 잡지 않게 한다
+        RentalTimeValidator.validate(request.rentAtHour(), request.rentAtMinute());
+        rentalApplyUseCase.apply(
+            apiUser.userId(),
+            request.itemId(),
+            request.count(),
+            request.rentAtHour(),
+            request.rentAtMinute(),
+            request.ignoreDuplicate()
+        );
+        return ApiResponse.success();
+    }
+
+    @Override
+    @PatchMapping("/histories/{rentalHistoryId}/return")
+    public ApiResponse<Void> returnRental(AppApiUser apiUser, @PathVariable Long rentalHistoryId) {
+        rentalHistoryService.returnRental(apiUser.userId(), rentalHistoryId);
+        return ApiResponse.success();
+    }
 }
diff --git a/api/app-api/src/main/java/kr/ac/kookmin/stream/api/app/welfare/rental/request/RentalApplyRequest.java b/api/app-api/src/main/java/kr/ac/kookmin/stream/api/app/welfare/rental/request/RentalApplyRequest.java
new file mode 100644
index 00000000..bb9fe1b1
--- /dev/null
+++ b/api/app-api/src/main/java/kr/ac/kookmin/stream/api/app/welfare/rental/request/RentalApplyRequest.java
@@ -0,0 +1,28 @@
+package kr.ac.kookmin.stream.api.app.welfare.rental.request;
+
+import jakarta.validation.constraints.Max;
+import jakarta.validation.constraints.Min;
+import jakarta.validation.constraints.NotNull;
+import jakarta.validation.constraints.Positive;
+
+public record RentalApplyRequest(
+    @NotNull(message = "대여할 물품을 선택해 주세요.")
+    Long itemId,
+
+    @NotNull(message = "대여 수량을 입력해 주세요.")
+    @Positive(message = "대여 수량은 1개 이상이어야 합니다.")
+    Integer count,
+
+    @NotNull(message = "대여 시작 시(hour)를 입력해 주세요.")
+    @Min(value = 0, message = "대여 시작 시(hour)는 0~23 사이여야 합니다.")
+    @Max(value = 23, message = "대여 시작 시(hour)는 0~23 사이여야 합니다.")
+    Integer rentAtHour,
+
+    @NotNull(message = "대여 시작 분(minute)을 입력해 주세요.")
+    @Min(value = 0, message = "대여 시작 분(minute)은 0~59 사이여야 합니다.")
+    @Max(value = 59, message = "대여 시작 분(minute)은 0~59 사이여야 합니다.")
+    Integer rentAtMinute,
+
+    @NotNull(message = "중복 대여 진행 여부를 입력해 주세요.")
+    Boolean ignoreDuplicate
+) {}
diff --git a/api/app-api/src/main/java/kr/ac/kookmin/stream/api/app/welfare/rental/usecase/RentalApplyUseCase.java b/api/app-api/src/main/java/kr/ac/kookmin/stream/api/app/welfare/rental/usecase/RentalApplyUseCase.java
new file mode 100644
index 00000000..d34219ec
--- /dev/null
+++ b/api/app-api/src/main/java/kr/ac/kookmin/stream/api/app/welfare/rental/usecase/RentalApplyUseCase.java
@@ -0,0 +1,44 @@
+package kr.ac.kookmin.stream.api.app.welfare.rental.usecase;
+
+import java.time.LocalDate;
+import java.time.LocalDateTime;
+import kr.ac.kookmin.stream.common.BusinessException;
+import kr.ac.kookmin.stream.common.DateUtil;
+import kr.ac.kookmin.stream.welfare.domain.fee.service.PayerService;
+import kr.ac.kookmin.stream.welfare.domain.rental.domain.Item;
+import kr.ac.kookmin.stream.welfare.domain.rental.domain.RentalErrorCode;
+import kr.ac.kookmin.stream.welfare.domain.rental.service.ItemService;
+import kr.ac.kookmin.stream.welfare.domain.rental.service.RentalHistoryService;
+import lombok.RequiredArgsConstructor;
+import org.springframework.stereotype.Component;
+import org.springframework.transaction.annotation.Transactional;
+
+/**
+ * 대여 신청. {@code fee}(회비 납부 확인)와 {@code rental}(재고 차감, 이력 생성) 두 도메인을 조합한다.
+ * 대여 시간(영업시간·점심시간) 검증은 DB에 닿지 않으므로 이 트랜잭션에 들어오기 전, 컨트롤러에서 끝낸다.
+ */
+@Component
+@RequiredArgsConstructor
+public class RentalApplyUseCase {
+
+    private final PayerService payerService;
+    private final ItemService itemService;
+    private final RentalHistoryService rentalHistoryService;
+
+    @Transactional
+    public void apply(Long memberId, Long itemId, int count, int rentAtHour, int rentAtMinute, boolean ignoreDuplicate) {
+        // 동시성 보호(락) 없이 진행한다 — 재고 경쟁, 중복 대여 경쟁 둘 다 이론적으로 남아있는
+        // 경합이다. 필요해지면 별도로 다시 도입한다(billilge-rental-apply-review-fixes.md 참고).
+        payerService.validatePayer(memberId);
+
+        if (!ignoreDuplicate && rentalHistoryService.existsActiveRental(itemId, memberId)) {
+            throw new BusinessException(RentalErrorCode.RENTAL_ITEM_DUPLICATED);
+        }
+
+        Item item = itemService.decreaseStock(itemId, count);
+
+        LocalDateTime now = LocalDateTime.now(DateUtil.KST);
+        LocalDateTime rentAt = LocalDate.now(DateUtil.KST).atTime(rentAtHour, rentAtMinute);
+        rentalHistoryService.create(item, memberId, count, now, rentAt);
+    }
+}
diff --git a/core/common/src/main/java/kr/ac/kookmin/stream/common/DateUtil.java b/core/common/src/main/java/kr/ac/kookmin/stream/common/DateUtil.java
index 5629d8a4..948a8cc8 100644
--- a/core/common/src/main/java/kr/ac/kookmin/stream/common/DateUtil.java
+++ b/core/common/src/main/java/kr/ac/kookmin/stream/common/DateUtil.java
@@ -1,6 +1,7 @@
 package kr.ac.kookmin.stream.common;
 
 import java.time.LocalDate;
+import java.time.ZoneId;
 import lombok.AccessLevel;
 import lombok.NoArgsConstructor;
 
@@ -10,6 +11,9 @@
 @NoArgsConstructor(access = AccessLevel.PRIVATE)
 public final class DateUtil {
 
+    /** 서버 기본 타임존에 기대지 않고 명시적으로 한국 표준시를 써야 하는 곳에 쓴다. */
+    public static final ZoneId KST = ZoneId.of("Asia/Seoul");
+
     private static final int FIRST_MONTH = 1;
     private static final int FIRST_DAY = 1;
 
diff --git a/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/fee/domain/FeeErrorCode.java b/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/fee/domain/FeeErrorCode.java
index 50a00db7..e3eb793f 100644
--- a/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/fee/domain/FeeErrorCode.java
+++ b/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/fee/domain/FeeErrorCode.java
@@ -15,7 +15,8 @@ public enum FeeErrorCode implements ErrorCode {
     INVALID_TRANSFER_STATUS(ErrorStatus.BAD_REQUEST, "유효하지 않은 납부 상태입니다."),
     FEE_REQUEST_NOT_FOUND(ErrorStatus.NOT_FOUND, "존재하지 않는 납부 확인 요청입니다."),
     FEE_REQUEST_ALREADY_REVIEWED(ErrorStatus.CONFLICT, "이미 처리된 납부 확인 요청입니다."),
-    FEE_TRANSFER_LINK_INVALID(ErrorStatus.INTERNAL_SERVER_ERROR, "송금 요청 URL이 생성되지 않았습니다. 관리자에게 문의해 주세요.");
+    FEE_TRANSFER_LINK_INVALID(ErrorStatus.INTERNAL_SERVER_ERROR, "송금 요청 URL이 생성되지 않았습니다. 관리자에게 문의해 주세요."),
+    MEMBER_IS_NOT_PAYER(ErrorStatus.BAD_REQUEST, "회비를 납부한 회원만 이용할 수 있습니다.");
 
     private final int status;
     private final String message;
diff --git a/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/fee/service/PayerService.java b/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/fee/service/PayerService.java
index f988a3e6..b9e168d3 100644
--- a/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/fee/service/PayerService.java
+++ b/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/fee/service/PayerService.java
@@ -6,4 +6,7 @@ public interface PayerService {
 
     // 확인요청 처리 결과를 납부자 명부(Payer)에 반영한다. PAID면 등록, 그 외(UNPAID)면 명부에서 제거한다.
     void sync(Long memberId, String name, String studentId, TransferStatus status);
+
+    // 회원이 납부자 명부에 등록돼 있는지 확인하고, 아니면 예외를 던진다(회비 납부 여부가 필요한 다른 도메인의 조건 확인용).
+    void validatePayer(Long memberId);
 }
diff --git a/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/fee/service/impl/PayerServiceImpl.java b/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/fee/service/impl/PayerServiceImpl.java
index 5ba1fb3f..74fc041d 100644
--- a/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/fee/service/impl/PayerServiceImpl.java
+++ b/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/fee/service/impl/PayerServiceImpl.java
@@ -1,5 +1,7 @@
 package kr.ac.kookmin.stream.welfare.domain.fee.service.impl;
 
+import kr.ac.kookmin.stream.common.BusinessException;
+import kr.ac.kookmin.stream.welfare.domain.fee.domain.FeeErrorCode;
 import kr.ac.kookmin.stream.welfare.domain.fee.domain.Payer;
 import kr.ac.kookmin.stream.welfare.domain.fee.domain.TransferStatus;
 import kr.ac.kookmin.stream.welfare.domain.fee.repository.PayerRepository;
@@ -36,4 +38,12 @@ public void sync(Long memberId, String name, String studentId, TransferStatus st
     private String enrollmentYearOf(String studentId) {
         return studentId.substring(0, 4);
     }
+
+    // 조회 쿼리가 1개라 트랜잭션을 걸지 않는다(PR#67/#69 원칙 — 조회니까 붙이는 게 아니라 실제 이득이 있을 때만 붙인다).
+    @Override
+    public void validatePayer(Long memberId) {
+        if (payerRepository.findByMemberId(memberId).isEmpty()) {
+            throw new BusinessException(FeeErrorCode.MEMBER_IS_NOT_PAYER);
+        }
+    }
 }
diff --git a/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/domain/Item.java b/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/domain/Item.java
index a10c5342..81923ab2 100644
--- a/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/domain/Item.java
+++ b/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/domain/Item.java
@@ -1,5 +1,6 @@
 package kr.ac.kookmin.stream.welfare.domain.rental.domain;
 
+import kr.ac.kookmin.stream.common.BusinessException;
 import lombok.AccessLevel;
 import lombok.AllArgsConstructor;
 import lombok.EqualsAndHashCode;
@@ -32,4 +33,12 @@ public static Item of(
         ReturnPolicy applicablePolicy = type == ItemType.RENTAL ? returnPolicy : null;
         return new Item(id, name, category, type, count, imageKey, applicablePolicy);
     }
+
+    /** 재고를 차감한다. 재고가 부족하면(0 밑으로 내려가면) 예외를 던진다. */
+    public void decreaseStock(int amount) {
+        if (amount > this.count) {
+            throw new BusinessException(RentalErrorCode.ITEM_OUT_OF_STOCK);
+        }
+        this.count -= amount;
+    }
 }
diff --git a/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/domain/RentalErrorCode.java b/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/domain/RentalErrorCode.java
index 23b0ace6..a577fd75 100644
--- a/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/domain/RentalErrorCode.java
+++ b/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/domain/RentalErrorCode.java
@@ -11,7 +11,13 @@
 @AllArgsConstructor
 public enum RentalErrorCode implements ErrorCode {
 
-    ITEM_INVALID_CURSOR(ErrorStatus.BAD_REQUEST, "유효하지 않은 커서입니다.");
+    ITEM_INVALID_CURSOR(ErrorStatus.BAD_REQUEST, "유효하지 않은 커서입니다."),
+    ITEM_NOT_FOUND(ErrorStatus.NOT_FOUND, "존재하지 않는 물품입니다."),
+    ITEM_OUT_OF_STOCK(ErrorStatus.BAD_REQUEST, "재고가 부족합니다."),
+    RENTAL_ITEM_DUPLICATED(ErrorStatus.BAD_REQUEST, "이미 대여 중인 물품입니다."),
+    INVALID_RENTAL_TIME_RANGE(ErrorStatus.BAD_REQUEST, "대여 가능 시간이 아니에요. 10시-17시 사이로 선택해 주세요."),
+    INVALID_RENTAL_TIME_LUNCH_BREAK(ErrorStatus.BAD_REQUEST, "점심시간(12시-13시)에는 대여가 불가능해요."),
+    RENTAL_NOT_FOUND(ErrorStatus.NOT_FOUND, "존재하지 않는 대여 이력입니다.");
 
     private final int status;
     private final String message;
diff --git a/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/domain/RentalHistory.java b/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/domain/RentalHistory.java
index f135e33f..93fab0dc 100644
--- a/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/domain/RentalHistory.java
+++ b/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/domain/RentalHistory.java
@@ -22,6 +22,25 @@ public class RentalHistory {
     private LocalDateTime rentAt;
     private LocalDateTime returnedAt;
 
+    /**
+     * 대여 신청으로 새 이력을 만든다. 소모품(반납 개념이 없는 물품)은 처음부터 반납 완료로,
+     * 대여품은 대여 중으로 시작한다 — 이 프로젝트엔 운영진이 수령을 확정해 주는 단계가 없어서,
+     * 레거시(billilge/backend) {@code RentalService.updateRentalStatus()}가 물품 인도 시점에 하던
+     * "소모품이면 RENTAL 대신 RETURNED" 분기를 신청 시점으로 그대로 옮겼다.
+     */
+    public static RentalHistory create(Item item, Long memberId, int rentedCount, LocalDateTime appliedAt, LocalDateTime rentAt) {
+        boolean returnable = item.getType() == ItemType.RENTAL;
+        RentalStatus status = returnable ? RentalStatus.RENTAL : RentalStatus.RETURNED;
+        LocalDateTime returnedAt = returnable ? null : appliedAt;
+        return new RentalHistory(null, item.getId(), memberId, null, null, status, rentedCount, appliedAt, rentAt, returnedAt);
+    }
+
+    /** 반납 신청 처리. 운영진의 최종 확인 단계가 없어 신청 즉시 반납 완료로 전이한다. */
+    public void markReturned(LocalDateTime returnedAt) {
+        this.rentalStatus = RentalStatus.RETURNED;
+        this.returnedAt = returnedAt;
+    }
+
     public static RentalHistory of(
         Long id,
         Long itemId,
diff --git a/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/repository/ItemRepository.java b/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/repository/ItemRepository.java
index 9747cf48..4022a086 100644
--- a/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/repository/ItemRepository.java
+++ b/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/repository/ItemRepository.java
@@ -2,6 +2,7 @@
 
 import java.util.Collection;
 import java.util.List;
+import java.util.Optional;
 import kr.ac.kookmin.stream.common.CursorSliceResult;
 import kr.ac.kookmin.stream.welfare.domain.rental.domain.Item;
 import kr.ac.kookmin.stream.welfare.domain.rental.domain.ItemCategory;
@@ -19,4 +20,8 @@ public interface ItemRepository {
     CursorSliceResult<Item> findSlice(ItemCategory category, String keyword, ItemCursor cursor, int size);
 
     List<Item> findAllByIds(Collection<Long> ids);
+
+    Optional<Item> findById(Long id);
+
+    Item save(Item item);
 }
diff --git a/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/repository/RentalHistoryRepository.java b/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/repository/RentalHistoryRepository.java
index 33721bb9..77b41c6d 100644
--- a/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/repository/RentalHistoryRepository.java
+++ b/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/repository/RentalHistoryRepository.java
@@ -1,6 +1,7 @@
 package kr.ac.kookmin.stream.welfare.domain.rental.repository;
 
 import java.util.List;
+import java.util.Optional;
 import kr.ac.kookmin.stream.welfare.domain.rental.domain.RentalHistory;
 import kr.ac.kookmin.stream.welfare.domain.rental.domain.RentalStatus;
 
@@ -12,4 +13,12 @@ public interface RentalHistoryRepository {
      * @param status 대여 상태. null이면 전체
      */
     List<RentalHistory> findAllByMemberId(Long memberId, RentalStatus status);
+
+    RentalHistory save(RentalHistory history);
+
+    /** 같은 회원이 같은 물품을 이미 대여 중인지(상태가 RENTAL인 이력이 있는지) 확인한다. */
+    boolean existsActiveRental(Long itemId, Long memberId);
+
+    /** 반납 신청 대상 조회. 본인 소유가 아니거나 대여 중 상태가 아니면 빈 값이다(둘 다 RENTAL_NOT_FOUND로 처리). */
+    Optional<RentalHistory> findRentalToReturn(Long id, Long memberId);
 }
diff --git a/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/service/ItemService.java b/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/service/ItemService.java
index 63448314..398241c8 100644
--- a/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/service/ItemService.java
+++ b/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/service/ItemService.java
@@ -15,4 +15,14 @@ public interface ItemService {
      * @param cursor   이전 페이지의 마지막 항목. null이면 첫 페이지
      */
     CursorSliceResult<Item> getItems(ItemCategory category, String keyword, ItemCursor cursor, int size);
+
+    /**
+     * 재고를 차감한다.
+     * <p>
+     * 동시성 보호(락)는 아직 없다 — 동시에 들어온 두 요청이 같은 물품의 재고를 동시에 통과해
+     * 재고가 음수로 내려갈 수 있는 경합이 이론적으로 남아있다. 이 프로젝트 규모에서 실제로
+     * 문제된 적은 없어 보이는 레거시(billilge/backend)와 같은 수준으로, 일단 보호 없이 간다
+     * (`billilge-rental-apply-review-fixes.md` 참고 — 필요해지면 별도로 다시 도입한다).
+     */
+    Item decreaseStock(Long itemId, int amount);
 }
diff --git a/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/service/RentalHistoryService.java b/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/service/RentalHistoryService.java
index 20aaac34..e981a9a1 100644
--- a/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/service/RentalHistoryService.java
+++ b/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/service/RentalHistoryService.java
@@ -1,6 +1,9 @@
 package kr.ac.kookmin.stream.welfare.domain.rental.service;
 
+import java.time.LocalDateTime;
 import java.util.List;
+import kr.ac.kookmin.stream.welfare.domain.rental.domain.Item;
+import kr.ac.kookmin.stream.welfare.domain.rental.domain.RentalHistory;
 import kr.ac.kookmin.stream.welfare.domain.rental.domain.RentalHistorySummary;
 import kr.ac.kookmin.stream.welfare.domain.rental.domain.RentalStatus;
 import kr.ac.kookmin.stream.welfare.domain.rental.domain.ReturnRequiredRental;
@@ -19,4 +22,16 @@ public interface RentalHistoryService {
      * 반납 정책이 없는 물품의 대여는 기한을 계산할 수 없어 제외한다.
      */
     List<ReturnRequiredRental> getReturnRequiredRentals(Long memberId);
+
+    /**
+     * 반납 신청. 본인 소유의 대여 중(RENTAL) 이력만 대상이며, 신청 즉시 반납 완료로 전이한다
+     * (운영진의 최종 확인 단계가 없어서다).
+     */
+    void returnRental(Long memberId, Long historyId);
+
+    /** 같은 회원이 같은 물품을 이미 대여 중인지(상태가 RENTAL인 이력이 있는지) 확인한다. */
+    boolean existsActiveRental(Long itemId, Long memberId);
+
+    /** 대여 신청으로 새 이력을 만들고 저장한다. */
+    RentalHistory create(Item item, Long memberId, int count, LocalDateTime appliedAt, LocalDateTime rentAt);
 }
diff --git a/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/service/RentalTimeValidator.java b/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/service/RentalTimeValidator.java
new file mode 100644
index 00000000..0ae3fc93
--- /dev/null
+++ b/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/service/RentalTimeValidator.java
@@ -0,0 +1,27 @@
+package kr.ac.kookmin.stream.welfare.domain.rental.service;
+
+import java.time.LocalTime;
+import kr.ac.kookmin.stream.common.BusinessException;
+import kr.ac.kookmin.stream.welfare.domain.rental.domain.RentalErrorCode;
+
+// 대여 신청 시각(영업시간 10~17시, 점심시간 12~13시 제외)을 검증한다.
+// fee 도메인의 FeeAmountCalculator/TossTransferLinkGenerator와 같은 패턴 — 상태 없는 순수 검증 로직은 정적 유틸로 둔다.
+public final class RentalTimeValidator {
+
+    private static final LocalTime OPEN = LocalTime.of(10, 0);
+    private static final LocalTime CLOSE = LocalTime.of(17, 0);
+    private static final LocalTime LUNCH_START = LocalTime.of(12, 0);
+    private static final LocalTime LUNCH_END = LocalTime.of(13, 0);
+
+    private RentalTimeValidator() {}
+
+    public static void validate(int hour, int minute) {
+        LocalTime rentalTime = LocalTime.of(hour, minute);
+        if (rentalTime.isBefore(OPEN) || rentalTime.isAfter(CLOSE)) {
+            throw new BusinessException(RentalErrorCode.INVALID_RENTAL_TIME_RANGE);
+        }
+        if (!rentalTime.isBefore(LUNCH_START) && rentalTime.isBefore(LUNCH_END)) {
+            throw new BusinessException(RentalErrorCode.INVALID_RENTAL_TIME_LUNCH_BREAK);
+        }
+    }
+}
diff --git a/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/service/impl/ItemServiceImpl.java b/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/service/impl/ItemServiceImpl.java
index 88aa630f..a5373542 100644
--- a/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/service/impl/ItemServiceImpl.java
+++ b/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/service/impl/ItemServiceImpl.java
@@ -1,13 +1,16 @@
 package kr.ac.kookmin.stream.welfare.domain.rental.service.impl;
 
+import kr.ac.kookmin.stream.common.BusinessException;
 import kr.ac.kookmin.stream.common.CursorSliceResult;
 import kr.ac.kookmin.stream.welfare.domain.rental.domain.Item;
 import kr.ac.kookmin.stream.welfare.domain.rental.domain.ItemCategory;
 import kr.ac.kookmin.stream.welfare.domain.rental.domain.ItemCursor;
+import kr.ac.kookmin.stream.welfare.domain.rental.domain.RentalErrorCode;
 import kr.ac.kookmin.stream.welfare.domain.rental.repository.ItemRepository;
 import kr.ac.kookmin.stream.welfare.domain.rental.service.ItemService;
 import lombok.RequiredArgsConstructor;
 import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
 
 @Service
 @RequiredArgsConstructor
@@ -20,4 +23,13 @@ class ItemServiceImpl implements ItemService {
     public CursorSliceResult<Item> getItems(ItemCategory category, String keyword, ItemCursor cursor, int size) {
         return itemRepository.findSlice(category, keyword, cursor, size);
     }
+
+    @Override
+    @Transactional
+    public Item decreaseStock(Long itemId, int amount) {
+        Item item = itemRepository.findById(itemId)
+            .orElseThrow(() -> new BusinessException(RentalErrorCode.ITEM_NOT_FOUND));
+        item.decreaseStock(amount);
+        return itemRepository.save(item);
+    }
 }
diff --git a/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/service/impl/RentalHistoryServiceImpl.java b/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/service/impl/RentalHistoryServiceImpl.java
index 327ec3f4..b009bcd4 100644
--- a/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/service/impl/RentalHistoryServiceImpl.java
+++ b/core/domain/welfare/src/main/java/kr/ac/kookmin/stream/welfare/domain/rental/service/impl/RentalHistoryServiceImpl.java
@@ -1,10 +1,14 @@
 package kr.ac.kookmin.stream.welfare.domain.rental.service.impl;
 
+import java.time.LocalDateTime;
 import java.util.List;
 import java.util.Map;
 import java.util.function.Function;
 import java.util.stream.Collectors;
+import kr.ac.kookmin.stream.common.BusinessException;
+import kr.ac.kookmin.stream.common.DateUtil;
 import kr.ac.kookmin.stream.welfare.domain.rental.domain.Item;
+import kr.ac.kookmin.stream.welfare.domain.rental.domain.RentalErrorCode;
 import kr.ac.kookmin.stream.welfare.domain.rental.domain.RentalHistory;
 import kr.ac.kookmin.stream.welfare.domain.rental.domain.RentalHistorySummary;
 import kr.ac.kookmin.stream.welfare.domain.rental.domain.RentalStatus;
@@ -62,4 +66,27 @@ private Map<Long, Item> findItemsOf(List<RentalHistory> histories) {
     private boolean hasDueAt(RentalHistory history, Item item) {
         return history.getRentAt() != null && item != null && item.getReturnPolicy() != null;
     }
+
+    // 조회(대상 확인) + 쓰기(상태 전이)가 원자적으로 묶여야 하므로 일반 트랜잭션이다.
+    @Override
+    @Transactional
+    public void returnRental(Long memberId, Long historyId) {
+        RentalHistory history = rentalHistoryRepository.findRentalToReturn(historyId, memberId)
+            .orElseThrow(() -> new BusinessException(RentalErrorCode.RENTAL_NOT_FOUND));
+        history.markReturned(LocalDateTime.now(DateUtil.KST));
+        rentalHistoryRepository.save(history);
+    }
+
+    // 단일 조회라 dirty-checking 이득이 없어 트랜잭션을 걸지 않는다. 대여 신청(RentalApplyUseCase)의
+    // 트랜잭션 안에서 호출되므로, 재고 락 조회 이후에 고정된 스냅샷을 그대로 공유해서 쓴다.
+    @Override
+    public boolean existsActiveRental(Long itemId, Long memberId) {
+        return rentalHistoryRepository.existsActiveRental(itemId, memberId);
+    }
+
+    @Override
+    @Transactional
+    public RentalHistory create(Item item, Long memberId, int count, LocalDateTime appliedAt, LocalDateTime rentAt) {
+        return rentalHistoryRepository.save(RentalHistory.create(item, memberId, count, appliedAt, rentAt));
+    }
 }
diff --git a/infrastructure/db/src/main/java/kr/ac/kookmin/stream/db/welfare/ItemRepositoryImpl.java b/infrastructure/db/src/main/java/kr/ac/kookmin/stream/db/welfare/ItemRepositoryImpl.java
index 3d130e47..17e89dbe 100644
--- a/infrastructure/db/src/main/java/kr/ac/kookmin/stream/db/welfare/ItemRepositoryImpl.java
+++ b/infrastructure/db/src/main/java/kr/ac/kookmin/stream/db/welfare/ItemRepositoryImpl.java
@@ -2,6 +2,7 @@
 
 import java.util.Collection;
 import java.util.List;
+import java.util.Optional;
 import kr.ac.kookmin.stream.common.CursorSliceResult;
 import kr.ac.kookmin.stream.welfare.domain.rental.domain.Item;
 import kr.ac.kookmin.stream.welfare.domain.rental.domain.ItemCategory;
@@ -39,6 +40,16 @@ public List<Item> findAllByIds(Collection<Long> ids) {
             .toList();
     }
 
+    @Override
+    public Optional<Item> findById(Long id) {
+        return itemJpaRepository.findById(id).map(ItemJpaEntity::toDomain);
+    }
+
+    @Override
+    public Item save(Item item) {
+        return itemJpaRepository.save(ItemJpaEntity.from(item)).toDomain();
+    }
+
     // 검색어를 "포함" 조건의 LIKE 패턴으로 바꾼다. 검색어 안의 와일드카드가 패턴으로 해석되지 않게 이스케이프한다
     private String toContainsPattern(String keyword) {
         String escaped = keyword
diff --git a/infrastructure/db/src/main/java/kr/ac/kookmin/stream/db/welfare/RentalHistoryJpaRepository.java b/infrastructure/db/src/main/java/kr/ac/kookmin/stream/db/welfare/RentalHistoryJpaRepository.java
index 4d3606e5..c6e7184a 100644
--- a/infrastructure/db/src/main/java/kr/ac/kookmin/stream/db/welfare/RentalHistoryJpaRepository.java
+++ b/infrastructure/db/src/main/java/kr/ac/kookmin/stream/db/welfare/RentalHistoryJpaRepository.java
@@ -1,6 +1,7 @@
 package kr.ac.kookmin.stream.db.welfare;
 
 import java.util.List;
+import java.util.Optional;
 import kr.ac.kookmin.stream.welfare.domain.rental.domain.RentalStatus;
 import org.springframework.data.jpa.repository.JpaRepository;
 import org.springframework.data.jpa.repository.Query;
@@ -18,4 +19,8 @@ List<RentalHistoryJpaEntity> findAllByMemberId(
         @Param("memberId") Long memberId,
         @Param("status") RentalStatus status
     );
+
+    boolean existsByItemIdAndMemberIdAndRentalStatus(Long itemId, Long memberId, RentalStatus rentalStatus);
+
+    Optional<RentalHistoryJpaEntity> findByIdAndMemberIdAndRentalStatus(Long id, Long memberId, RentalStatus rentalStatus);
 }
diff --git a/infrastructure/db/src/main/java/kr/ac/kookmin/stream/db/welfare/RentalHistoryRepositoryImpl.java b/infrastructure/db/src/main/java/kr/ac/kookmin/stream/db/welfare/RentalHistoryRepositoryImpl.java
index 8dfe1494..9f56e190 100644
--- a/infrastructure/db/src/main/java/kr/ac/kookmin/stream/db/welfare/RentalHistoryRepositoryImpl.java
+++ b/infrastructure/db/src/main/java/kr/ac/kookmin/stream/db/welfare/RentalHistoryRepositoryImpl.java
@@ -1,6 +1,7 @@
 package kr.ac.kookmin.stream.db.welfare;
 
 import java.util.List;
+import java.util.Optional;
 import kr.ac.kookmin.stream.welfare.domain.rental.domain.RentalHistory;
 import kr.ac.kookmin.stream.welfare.domain.rental.domain.RentalStatus;
 import kr.ac.kookmin.stream.welfare.domain.rental.repository.RentalHistoryRepository;
@@ -19,4 +20,20 @@ public List<RentalHistory> findAllByMemberId(Long memberId, RentalStatus status)
             .map(RentalHistoryJpaEntity::toDomain)
             .toList();
     }
+
+    @Override
+    public RentalHistory save(RentalHistory history) {
+        return rentalHistoryJpaRepository.save(RentalHistoryJpaEntity.from(history)).toDomain();
+    }
+
+    @Override
+    public boolean existsActiveRental(Long itemId, Long memberId) {
+        return rentalHistoryJpaRepository.existsByItemIdAndMemberIdAndRentalStatus(itemId, memberId, RentalStatus.RENTAL);
+    }
+
+    @Override
+    public Optional<RentalHistory> findRentalToReturn(Long id, Long memberId) {
+        return rentalHistoryJpaRepository.findByIdAndMemberIdAndRentalStatus(id, memberId, RentalStatus.RENTAL)
+            .map(RentalHistoryJpaEntity::toDomain);
+    }
 }