diff --git a/src/main/java/github/benjamin/equipreservebackend/vo/DeviceUserVO.java b/src/main/java/github/benjamin/equipreservebackend/vo/DeviceUserVO.java
index ede3f59..1d74b1d 100644
--- a/src/main/java/github/benjamin/equipreservebackend/vo/DeviceUserVO.java
+++ b/src/main/java/github/benjamin/equipreservebackend/vo/DeviceUserVO.java
@@ -1,6 +1,9 @@
 package github.benjamin.equipreservebackend.vo;
 
+import com.fasterxml.jackson.databind.annotation.JsonSerialize;
+import com.fasterxml.jackson.databind.ser.std.ToStringSerializer;
 import github.benjamin.equipreservebackend.entity.Device;
+import github.benjamin.equipreservebackend.entity.User;
 import lombok.Data;
 import lombok.NoArgsConstructor;
 
@@ -8,6 +11,7 @@ import lombok.NoArgsConstructor;
 @NoArgsConstructor
 public class DeviceUserVO {
 
+    @JsonSerialize(using = ToStringSerializer.class)
     private Long deviceId;
     private String name;
     private String usageRequirement;
diff --git a/src/main/java/github/benjamin/equipreservebackend/vo/LoginResponse.java b/src/main/java/github/benjamin/equipreservebackend/vo/LoginResponse.java
index 81aaccf..ba7ad7a 100644
--- a/src/main/java/github/benjamin/equipreservebackend/vo/LoginResponse.java
+++ b/src/main/java/github/benjamin/equipreservebackend/vo/LoginResponse.java
@@ -1,5 +1,7 @@
 package github.benjamin.equipreservebackend.vo;
 
+import com.fasterxml.jackson.databind.annotation.JsonSerialize;
+import com.fasterxml.jackson.databind.ser.std.ToStringSerializer;
 import github.benjamin.equipreservebackend.entity.Role;
 import lombok.AllArgsConstructor;
 import lombok.Data;
@@ -10,6 +12,7 @@ import java.util.List;
 @AllArgsConstructor
 public class LoginResponse {
 
+    @JsonSerialize(using = ToStringSerializer.class)
     private Long userId;
     private String name;
     private List<String> roles;