diff --git a/src/main/java/ssu/eatssu/domain/auth/security/CustomUserDetailsService.java b/src/main/java/ssu/eatssu/domain/auth/security/CustomUserDetailsService.java
index 3e52882..3b1f6a5 100644
--- a/src/main/java/ssu/eatssu/domain/auth/security/CustomUserDetailsService.java
+++ b/src/main/java/ssu/eatssu/domain/auth/security/CustomUserDetailsService.java
@@ -17,9 +17,10 @@ public class CustomUserDetailsService implements UserDetailsService {
 
     private final UserRepository userRepository;
 
+    // OrderByIdAsc로 해줌으로써 처음 생성된 계정으로 연결된다.
     @Override
     public UserDetails loadUserByUsername(String username) {
-        User user = userRepository.findByEmail(username)
+        User user = userRepository.findFirstByEmailOrderByIdAsc(username)
                                   .orElseThrow(() -> new BaseException(BaseResponseStatus.NOT_FOUND_USER));
         return new CustomUserDetails(user);
     }
diff --git a/src/main/java/ssu/eatssu/domain/auth/service/OAuthService.java b/src/main/java/ssu/eatssu/domain/auth/service/OAuthService.java
index 2d6e7ad..1b46af8 100644
--- a/src/main/java/ssu/eatssu/domain/auth/service/OAuthService.java
+++ b/src/main/java/ssu/eatssu/domain/auth/service/OAuthService.java
@@ -34,7 +34,8 @@ public class OAuthService {
 
     public Tokens kakaoLogin(KakaoLoginRequest request) {
         User user = userRepository.findByProviderId(request.providerId())
-                                  .orElseGet(() -> userService.join(request.email(), KAKAO, request.providerId()));
+                                  .orElseGet(() -> userRepository.findFirstByEmailOrderByIdAsc(request.email())
+                                          .orElseGet(() -> userService.join(request.email(), KAKAO, request.providerId())));
 
         return generateOauthJwtTokens(user.getEmail(), KAKAO, request.providerId());
     }
@@ -44,11 +45,11 @@ public Tokens kakaoLogin(KakaoLoginRequest request) {
      */
     public Tokens kakaoLoginV2(KakaoLoginRequestV2 request) {
         User user = userRepository.findByProviderId(request.providerId())
-                .orElseGet(() -> userService.joinV2(request.email(), KAKAO, request.providerId(),request.deviceType()));
+                .orElseGet(() -> userRepository.findFirstByEmailOrderByIdAsc(request.email())
+                        .orElseGet(() -> userService.joinV2(request.email(), KAKAO, request.providerId(),request.deviceType())));
+
+        user.updateDeviceType(request.deviceType());
 
-        if (user.getDeviceType() == null) {
-           user.updateDeviceType(request.deviceType());
-        }
 
         return generateOauthJwtTokens(user.getEmail(), KAKAO, request.providerId());
     }
@@ -58,7 +59,8 @@ public Tokens appleLogin(AppleLoginRequest request) {
         OAuthInfo oAuthInfo = appleAuthenticator.getOAuthInfoByIdentityToken(request.identityToken());
 
         User user = userRepository.findByProviderId(oAuthInfo.providerId())
-                                  .orElseGet(() -> userService.join(oAuthInfo.email(), APPLE, oAuthInfo.providerId()));
+                                  .orElseGet(() -> userRepository.findFirstByEmailOrderByIdAsc(oAuthInfo.email())
+                                          .orElseGet(() -> userService.join(oAuthInfo.email(), APPLE, oAuthInfo.providerId())));
 
         updateAppleUserEmail(user, oAuthInfo.email());
 
@@ -72,13 +74,12 @@ public Tokens appleLoginV2(AppleLoginRequestV2 request) {
         OAuthInfo oAuthInfo = appleAuthenticator.getOAuthInfoByIdentityToken(request.identityToken());
 
         User user = userRepository.findByProviderId(oAuthInfo.providerId())
-                .orElseGet(() -> userService.joinV2(oAuthInfo.email(), APPLE, oAuthInfo.providerId(),request.deviceType()));
+                .orElseGet(() -> userRepository.findFirstByEmailOrderByIdAsc(oAuthInfo.email())
+                        .orElseGet(() -> userService.joinV2(oAuthInfo.email(), APPLE, oAuthInfo.providerId(),request.deviceType())));
 
         updateAppleUserEmail(user, oAuthInfo.email());
 
-        if (user.getDeviceType() == null) {
-            user.updateDeviceType(request.deviceType());
-        }
+        user.updateDeviceType(request.deviceType());
 
         return generateOauthJwtTokens(user.getEmail(), APPLE, oAuthInfo.providerId());
     }
diff --git a/src/main/java/ssu/eatssu/domain/user/entity/User.java b/src/main/java/ssu/eatssu/domain/user/entity/User.java
index 1013598..912d212 100644
--- a/src/main/java/ssu/eatssu/domain/user/entity/User.java
+++ b/src/main/java/ssu/eatssu/domain/user/entity/User.java
@@ -123,6 +123,6 @@ public void updateDepartment(Department department) {
         this.department = department;
     }
 
-    // 회원 가입 v2 마이그레이션을 위한 메서드 (원래는 가입시 DeviceType을 받아야 합니다.)
+    // 추후에 기종이 바뀌더라도 업데이트합니다. + V1-> V2 마이그레이션을 수행하는 역할을 하기도 합니다.
     public void updateDeviceType(DeviceType deviceType) { this.deviceType = deviceType; }
 }
diff --git a/src/main/java/ssu/eatssu/domain/user/repository/UserRepository.java b/src/main/java/ssu/eatssu/domain/user/repository/UserRepository.java
index fbc10d2..de6fa15 100644
--- a/src/main/java/ssu/eatssu/domain/user/repository/UserRepository.java
+++ b/src/main/java/ssu/eatssu/domain/user/repository/UserRepository.java
@@ -13,9 +13,7 @@ public interface UserRepository extends JpaRepository<User, Long> {
 
     boolean existsByNickname(String nickname);
 
-    Optional<User> findByEmail(String email);
-
     Optional<User> findByProviderId(String providerId);
 
-    Optional<User> findByNickname(String nickname);
+    Optional<User> findFirstByEmailOrderByIdAsc(String email);
 }
diff --git a/src/main/resources/application-dev.yml b/src/main/resources/application-dev.yml
index c328707..e201296 100644
--- a/src/main/resources/application-dev.yml
+++ b/src/main/resources/application-dev.yml
@@ -41,8 +41,8 @@ spring:
 jwt:
   secret:
     key: ${EATSSU_JWT_SECRET_DEV}
-  token-validity-in-seconds: 86400
-  refresh-token-validity-in-seconds: 604800
+  token-validity-in-seconds: 60
+  refresh-token-validity-in-seconds: 180
 
 #S3
 cloud: