diff --git a/app/src/main/java/com/example/tampopo_client/resources/ActivitiesResource.java b/app/src/main/java/com/example/tampopo_client/resources/ActivitiesResource.java
index c30407e..cef31d5 100644
--- a/app/src/main/java/com/example/tampopo_client/resources/ActivitiesResource.java
+++ b/app/src/main/java/com/example/tampopo_client/resources/ActivitiesResource.java
@@ -2,6 +2,7 @@
 
 import com.example.tampopo_client.models.Activity;
 
+import java.util.HashMap;
 import java.util.List;
 
 import retrofit2.Call;
@@ -15,7 +16,7 @@
 
 public interface ActivitiesResource {
     @GET("users/{user_id}/activities")
-    Call<List<Activity>> getActivities(@Path("user_id") String userId, @Query("filter") String filter);
+    Call<HashMap<String, Activity>> getActivities(@Path("user_id") String userId, @Query("filter") String filter);
 
     @POST("users/{user_id}/activities")
     @FormUrlEncoded
diff --git a/app/src/main/java/com/example/tampopo_client/viewmodels/ActivityViewModel.java b/app/src/main/java/com/example/tampopo_client/viewmodels/ActivityViewModel.java
index 08364f9..dcf1a07 100644
--- a/app/src/main/java/com/example/tampopo_client/viewmodels/ActivityViewModel.java
+++ b/app/src/main/java/com/example/tampopo_client/viewmodels/ActivityViewModel.java
@@ -12,6 +12,8 @@
 import java.time.LocalDateTime;
 import java.time.format.DateTimeFormatter;
 import java.util.ArrayList;
+import java.util.Collection;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 
@@ -208,23 +210,23 @@
      * @param callback アクティビティが取得された後に呼び出されるコールバック
      */
     private void pullLatestActivity(String userId, ActivitiesResource resource, ActivityFetchCallback callback) {
-        Call<List<Activity>> fetchActivityCall = resource.getActivities(userId, "LATEST");
-        fetchActivityCall.enqueue(new Callback<List<Activity>>() {
+        Call<HashMap<String, Activity>> fetchActivityCall = resource.getActivities(userId, "LATEST");
+        fetchActivityCall.enqueue(new Callback<HashMap<String, Activity>>() {
             @Override
-            public void onResponse(@NonNull Call<List<Activity>> call, @NonNull Response<List<Activity>> response) {
+            public void onResponse(@NonNull Call<HashMap<String, Activity>> call, @NonNull Response<HashMap<String, Activity>> response) {
                 if (response.isSuccessful()) {
-                    List<Activity> activities = response.body(); // アクティビティが存在しない場合は空のリスト
+                    Collection<Activity> activities = response.body().values(); // アクティビティが存在しない場合は空のリスト
                     if (activities == null || activities.isEmpty()) {
                         return;
                     }
 
-                    Activity latestActivity = activities.get(0);
+                    Activity latestActivity = activities.iterator().next();
                     callback.onSuccess(latestActivity);
                 }
             }
 
             @Override
-            public void onFailure(@NonNull Call<List<Activity>> call, @NonNull Throwable t) {
+            public void onFailure(@NonNull Call<HashMap<String, Activity>> call, @NonNull Throwable t) {
                 Log.e(ActivityViewModel.class.getSimpleName(), "An error has occurred while fetching the latest activity.", t);
 
                 callback.onFailure(t);