diff --git a/src/main/java/com/example/cosmos_serversb/jsons/UsersMapJson.java b/src/main/java/com/example/cosmos_serversb/jsons/UsersMapJson.java
new file mode 100644
index 0000000..c44487a
--- /dev/null
+++ b/src/main/java/com/example/cosmos_serversb/jsons/UsersMapJson.java
@@ -0,0 +1,29 @@
+package com.example.cosmos_serversb.jsons;
+
+import com.example.cosmos_serversb.entities.Group;
+import com.example.cosmos_serversb.entities.User;
+
+import java.util.ArrayList;
+import java.util.Set;
+
+public class UsersMapJson {
+    private ArrayList<UidUriJson> users = new ArrayList<>();
+
+    public UsersMapJson(Group group) {
+        changeUsersMap(group.getMembers());
+    }
+
+    public ArrayList<UidUriJson> getUsers() {
+        return users;
+    }
+
+    public void setUsers(ArrayList<UidUriJson> users) {
+        this.users = users;
+    }
+
+    private void changeUsersMap(Set set) {
+        for (User user : (Set<User>) set) {
+            users.add(new UidUriJson(user));
+        }
+    }
+}
diff --git a/src/main/java/com/example/cosmos_serversb/models/Groups.java b/src/main/java/com/example/cosmos_serversb/models/Groups.java
index 804a7dd..506c6b2 100644
--- a/src/main/java/com/example/cosmos_serversb/models/Groups.java
+++ b/src/main/java/com/example/cosmos_serversb/models/Groups.java
@@ -84,14 +84,15 @@
         return null;
     }
 
-    public static HashMap<String, String> addMember(String gId, String uId){
+    public static UsersMapJson addMember(String gId, String uId){
         Session session = SessionManager.getInstance().getSession();
         Group editGroup = session.load(Group.class, gId);
         if(editGroup != null) {
             editGroup.addMember(uId);
             session.update(editGroup);
         }
-        return null;//HashMapへの変更が必要
+        UsersMapJson usersMapJson = new UsersMapJson(editGroup);
+        return usersMapJson;
     }
 
     public static HashMap<String, String> deleteMember(String gId, String uId){