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 455723a..fb6ca60 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
@@ -64,7 +64,7 @@
         userResource = retrofit.create(UserResource.class);
 
         friendToActivitiesLiveData = new HashMap<>();
-        friendUserIdsLiveData = new MutableLiveData<>(List.of());
+        friendUserIdsLiveData = new MutableLiveData<>(new ArrayList<>());
         myLatestActivityLiveData = new MutableLiveData<>(null);
 
         userActivityStatusChangeListeners = new ArrayList<>();
@@ -109,8 +109,9 @@
             });
 
             // 自分のフレンドの最新のアクティビティを取得して更新する
-            if (friendUserIdsLiveData.isInitialized() && friendUserIdsLiveData.getValue() != null) {
-                for (String userId : friendUserIdsLiveData.getValue()) {
+            List<String> friendUserIds = friendUserIdsLiveData.getValue();
+            if (friendUserIds != null) {
+                for (String userId : friendUserIds) {
                     pullLatestActivity(userId, activitiesResource, new ActivityFetchCallback() {
                         @Override
                         public void onSuccess(Activity activity) {
@@ -119,17 +120,14 @@
 
                         @Override
                         public void onFailure(Throwable throwable) {
-                            Log.e(ActivityViewModel.class.getSimpleName(), "An error has occurred while fetching friend's latest activity.", throwable);
+                            Log.e(ActivityViewModel.class.getSimpleName(), "An error has occurred while fetching friend's latest activity for " + userId, throwable);
                         }
                     });
                 }
             }
 
-            if (friendUserIdsLiveData.isInitialized()) {
-                // 最新のフレンドのユーザーIDを取得して更新する
-                // TODO: 適切なコールバックを使う必要あり
-                pullLatestFriendUserIds(myUserId, myToken);
-            }
+            // 最新のフレンドのユーザーIDを取得して更新する
+            pullLatestFriendUserIds(myUserId, myToken);
         };
     }
 
@@ -141,7 +139,7 @@
      */
     private void updateFriendToActivitiesLiveData(Activity latestActivity, String userId) {
         if (friendToActivitiesLiveData.get(userId) == null) {
-            friendToActivitiesLiveData.put(userId, new MutableLiveData<>(List.of()));
+            friendToActivitiesLiveData.put(userId, new MutableLiveData<>(new ArrayList<>()));
         }
         MutableLiveData<List<Activity>> userActivitiesLiveData = friendToActivitiesLiveData.get(userId);
         assert userActivitiesLiveData != null;
@@ -151,7 +149,8 @@
         if (userActivities == null || userActivities.isEmpty()) {
             userActivitiesLiveData.postValue(List.of(latestActivity));
         } else {
-            if (userActivities.get(0).getActivityId().equals(latestActivity.getActivityId())) {
+            // 内容が同じなら更新しない（不要なUI更新を避ける）
+            if (userActivities.get(0).getText().equals(latestActivity.getText())) {
                 return;
             }
 
@@ -167,10 +166,6 @@
      * @param newActivity 新しいアクティビティのテキスト
      */
     public void createActivity(String userId, String token, String newActivity) {
-        if (!myLatestActivityLiveData.isInitialized()) {
-            return;
-        }
-
         Call<String> createActivityCall = activitiesResource.addActivity(userId, token, newActivity);
         createActivityCall.enqueue(new Callback<String>() {
             @Override
@@ -218,7 +213,7 @@
         fetchActivityCall.enqueue(new Callback<HashMap<String, Activity>>() {
             @Override
             public void onResponse(@NonNull Call<HashMap<String, Activity>> call, @NonNull Response<HashMap<String, Activity>> response) {
-                if (response.isSuccessful()) {
+                if (response.isSuccessful() && response.body() != null) {
                     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;
@@ -261,28 +256,20 @@
             @Override
             public void onResponse(@NonNull Call<List<String>> call, @NonNull Response<List<String>> response) {
                 if (response.isSuccessful()) {
-
-                    // MEMO: 入れ込んだだけ
-                    // フレンドのIDをアクティビティ更新順に並べ替える
-                    List<String> friendUserIds = friendUserIdsLiveData.getValue();
-                    if (friendUserIds == null || !friendUserIds.equals(response.body())) {
-                        friendUserIdsLiveData.postValue(response.body());
+                    List<String> friendUserIds = response.body();
+                    if (friendUserIds != null && !friendUserIds.equals(friendUserIdsLiveData.getValue())) {
+                        friendUserIdsLiveData.postValue(friendUserIds);
+                        
+                        // 並び替えロジック
                         SortedSet<Friend> friends = new TreeSet<>(new Friend.UpdateTimeComparator());
-
-                        assert friendUserIds != null;
-                        friendUserIds.forEach(userId -> {
-                            List<Activity> activities = getActivitiesLiveDataFromUserId(userId).getValue();
-                            if (activities == null || activities.isEmpty()) {
-                                return;
+                        for (String id : friendUserIds) {
+                            MutableLiveData<List<Activity>> ld = friendToActivitiesLiveData.get(id);
+                            if (ld != null && ld.getValue() != null && !ld.getValue().isEmpty()) {
+                                friends.add(new Friend(id, ld.getValue().get(0).getUpdateTime()));
                             }
-
-                            Activity latestActivity = activities.get(0);
-                            friends.add(new Friend(userId, latestActivity.getUpdateTime()));
-                        });
-
-                        // 並び替えたフレンドのユーザーIDを順番に格納して更新する
+                        }
                         sortedFriendUserIds.clear();
-                        friends.forEach(friend -> sortedFriendUserIds.add(friend.getUserId()));
+                        friends.forEach(f -> sortedFriendUserIds.add(f.getUserId()));
                     }
                 }
             }
@@ -306,7 +293,7 @@
      */
     public MutableLiveData<List<Activity>> getActivitiesLiveDataFromUserId(String userId) {
         if (!friendToActivitiesLiveData.containsKey(userId)) {
-            friendToActivitiesLiveData.put(userId, new MutableLiveData<>());
+            friendToActivitiesLiveData.put(userId, new MutableLiveData<>(new ArrayList<>()));
         }
         return friendToActivitiesLiveData.get(userId);
     }
@@ -355,7 +342,7 @@
         public static class UpdateTimeComparator implements Comparator<Friend> {
             @Override
             public int compare(Friend o1, Friend o2) {
-                return o1.getLatestUpdateTime().compareTo(o2.getLatestUpdateTime());
+                return o2.getLatestUpdateTime().compareTo(o1.getLatestUpdateTime()); // 降順（新しい順）
             }
         }
     }