diff --git a/crates/voicevox_core/src/engine/open_jtalk.rs b/crates/voicevox_core/src/engine/open_jtalk.rs
index ad1f8c19e..de3fd73dc 100644
--- a/crates/voicevox_core/src/engine/open_jtalk.rs
+++ b/crates/voicevox_core/src/engine/open_jtalk.rs
@@ -128,7 +128,13 @@ pub(crate) mod blocking {
     }
 
     impl Inner {
-        // FIXME: 中断可能にする
+        // TODO: 中断可能にする
+        pub(super) fn unload_user_dict(&self) -> crate::result::Result<()> {
+            let Resources { mecab, .. } = &mut *self.resources.lock().unwrap();
+            mecab.load_with_userdic(&self.dict_dir, None)
+        }
+
+        // TODO: 中断可能にする
         pub(super) fn use_user_dict(&self, words: &str) -> crate::result::Result<()> {
             let result = {
                 // ユーザー辞書用のcsvを作成
@@ -210,6 +216,9 @@ pub(crate) mod tokio {
             user_dict: &crate::tokio::UserDict,
         ) -> crate::result::Result<()> {
             let inner = self.0 .0.clone();
+            if user_dict.is_empty() {
+                return crate::task::asyncify(move || inner.unload_user_dict()).await;
+            }
             let words = user_dict.to_mecab_format();
             crate::task::asyncify(move || inner.use_user_dict(&words)).await
         }
diff --git a/crates/voicevox_core/src/user_dict/dict.rs b/crates/voicevox_core/src/user_dict/dict.rs
index 6997620f0..3ac5c9a39 100644
--- a/crates/voicevox_core/src/user_dict/dict.rs
+++ b/crates/voicevox_core/src/user_dict/dict.rs
@@ -99,6 +99,11 @@ pub(crate) mod blocking {
                 "\n",
             )
         }
+
+        /// ユーザー辞書が空かどうかを返す。
+        pub(crate) fn is_empty(&self) -> bool {
+            self.words.lock().unwrap().is_empty()
+        }
     }
 }
 
@@ -174,5 +179,10 @@ pub(crate) mod tokio {
         pub(crate) fn to_mecab_format(&self) -> String {
             self.0.to_mecab_format()
         }
+
+        /// ユーザー辞書が空かどうかを返す。
+        pub(crate) fn is_empty(&self) -> bool {
+            self.0.is_empty()
+        }
     }
 }