diff --git a/src/components/Sing/ToolBar/ToolBar.vue b/src/components/Sing/ToolBar/ToolBar.vue
index a9ea7b3a82..1b7112b68c 100644
--- a/src/components/Sing/ToolBar/ToolBar.vue
+++ b/src/components/Sing/ToolBar/ToolBar.vue
@@ -190,6 +190,7 @@ import {
 import CharacterMenuButton from "@/components/Sing/CharacterMenuButton/MenuButton.vue";
 import { useHotkeyManager } from "@/plugins/hotkeyPlugin";
 import { SequencerEditTarget } from "@/store/type";
+import { getNoteDuration } from "@/sing/domain";
 
 const store = useStore();
 
@@ -431,9 +432,34 @@ const goToZero = () => {
   void store.dispatch("SET_PLAYHEAD_POSITION", { position: 0 });
 };
 
-const { isLoopEnabled, setLoopEnabled } = useLoopControl();
-const toggleLoop = () => {
-  void setLoopEnabled(!isLoopEnabled.value);
+const {
+  isLoopEnabled,
+  setLoopEnabled,
+  setLoopRange,
+  loopStartTick,
+  loopEndTick,
+} = useLoopControl();
+
+const toggleLoop = async () => {
+  // ループが存在しない場合は見える範囲の1小節でループを作成
+  if (loopStartTick.value === loopEndTick.value) {
+    const sequencerBodyElement = document.querySelector(".sequencer-body");
+    if (!sequencerBodyElement) return;
+    const currentPosition = store.getters.GET_PLAYHEAD_POSITION();
+    const timeSignature = store.state.timeSignatures[0];
+    const oneMeasureTicks =
+      getNoteDuration(timeSignature.beatType, store.state.tpqn) *
+      timeSignature.beats;
+    const measureNumber = Math.floor(currentPosition / oneMeasureTicks);
+    const startTick = measureNumber * oneMeasureTicks;
+    const endTick = startTick + oneMeasureTicks;
+
+    await setLoopRange(startTick, endTick);
+    await setLoopEnabled(true);
+  } else {
+    // すでにループが存在する場合は単純に有効/無効を切り替え
+    await setLoopEnabled(!isLoopEnabled.value);
+  }
 };
 
 const volume = computed({
diff --git a/src/domain/project/index.ts b/src/domain/project/index.ts
index 3f541af269..995d144c8e 100644
--- a/src/domain/project/index.ts
+++ b/src/domain/project/index.ts
@@ -302,6 +302,17 @@ export const migrateProjectFileObject = async (
     projectData.song.trackOrder = Object.keys(newTracks);
   }
 
+  // FIXME: 0.21.0 のマイグレーション
+  //if (semver.satisfies(projectAppVersion, "<0.21.0", semverSatisfiesOptions)) {
+  if (!("loop" in projectData.song)) {
+    projectData.song.loop = {
+      startTick: 0,
+      endTick: 0,
+      isLoopEnabled: false,
+    };
+  }
+  //}
+
   // Validation check
   // トークはvalidateTalkProjectで検証する
   // ソングはSET_SCOREの中の`isValidScore`関数で検証される
diff --git a/src/domain/project/schema.ts b/src/domain/project/schema.ts
index 86ae436992..a4d499ec39 100644
--- a/src/domain/project/schema.ts
+++ b/src/domain/project/schema.ts
@@ -119,7 +119,11 @@ export const projectSchema = z.object({
     timeSignatures: z.array(timeSignatureSchema),
     tracks: z.record(trackIdSchema, trackSchema),
     trackOrder: z.array(trackIdSchema),
-    loop: loopSchema,
+    loop: z.object({
+      startTick: z.number(),
+      endTick: z.number(),
+      isLoopEnabled: z.boolean(),
+    }),
   }),
 });
 
diff --git a/src/sing/domain.ts b/src/sing/domain.ts
index d07cdb046d..e7c008f398 100644
--- a/src/sing/domain.ts
+++ b/src/sing/domain.ts
@@ -342,20 +342,6 @@ export function createDefaultTrack(): Track {
   };
 }
 
-export function createDefaultLoop(): Loop {
-  const defaultEndTick = getMeasureDuration(
-    DEFAULT_BEATS,
-    DEFAULT_BEAT_TYPE,
-    DEFAULT_TPQN,
-  );
-  console.log("defaultEndTick", defaultEndTick);
-  return {
-    isLoopEnabled: false,
-    startTick: 0,
-    endTick: defaultEndTick,
-  };
-}
-
 export function getSnapTypes(tpqn: number) {
   return getRepresentableNoteTypes(tpqn).filter((value) => {
     return value <= MAX_SNAP_TYPE;
diff --git a/src/store/project.ts b/src/store/project.ts
index e927cb3933..e8103b617f 100755
--- a/src/store/project.ts
+++ b/src/store/project.ts
@@ -22,7 +22,6 @@ import {
   createDefaultTempo,
   createDefaultTimeSignature,
   createDefaultTrack,
-  createDefaultLoop,
   DEFAULT_TPQN,
 } from "@/sing/domain";
 import { EditorType } from "@/type/preload";
@@ -62,7 +61,7 @@ const applySongProjectToStore = async (
   actions: DotNotationDispatch<AllActions>,
   songProject: LatestProjectType["song"],
 ) => {
-  const { tpqn, tempos, timeSignatures, tracks, trackOrder } = songProject;
+  const { tpqn, tempos, timeSignatures, tracks, trackOrder, loop } = songProject;
 
   await actions.SET_TPQN({ tpqn });
   await actions.SET_TEMPOS({ tempos });
@@ -76,6 +75,11 @@ const applySongProjectToStore = async (
       }),
     ),
   });
+  await actions.SET_LOOP_ENABLED({ isLoopEnabled: loop.isLoopEnabled });
+  await actions.SET_LOOP_RANGE({
+    loopStartTick: loop.startTick,
+    loopEndTick: loop.endTick,
+  });
 };
 
 export const projectStore = createPartialStore<ProjectStoreTypes>({
@@ -129,14 +133,6 @@ export const projectStore = createPartialStore<ProjectStoreTypes>({
         await context.actions.SET_TIME_SIGNATURES({
           timeSignatures: [createDefaultTimeSignature(1)],
         });
-        const defaultLoop = createDefaultLoop();
-        await context.actions.SET_LOOP_ENABLED({
-          isLoopEnabled: defaultLoop.isLoopEnabled,
-        });
-        await context.actions.SET_LOOP_RANGE({
-          loopStartTick: defaultLoop.startTick,
-          loopEndTick: defaultLoop.endTick,
-        });
         const trackId = TrackId(crypto.randomUUID());
         await context.actions.SET_TRACKS({
           tracks: new Map([[trackId, createDefaultTrack()]]),
@@ -159,6 +155,7 @@ export const projectStore = createPartialStore<ProjectStoreTypes>({
       if (characterInfos == undefined)
         throw new Error("characterInfos == undefined");
 
+      console.log(migrateProjectFileObject);
       const parsedProjectData = await migrateProjectFileObject(projectData, {
         fetchMoraData: (payload) => actions.FETCH_MORA_DATA(payload),
         voices: characterInfos.flatMap((characterInfo) =>
diff --git a/src/store/singing.ts b/src/store/singing.ts
index 30d895bccc..e149356749 100644
--- a/src/store/singing.ts
+++ b/src/store/singing.ts
@@ -78,7 +78,6 @@ import {
   createDefaultTrack,
   createDefaultTempo,
   createDefaultTimeSignature,
-  createDefaultLoop,
   isValidNotes,
   isValidTrack,
   SEQUENCER_MIN_NUM_MEASURES,
@@ -475,9 +474,9 @@ export const singingStoreState: SingingStoreState = {
   nowAudioExporting: false,
   cancellationOfAudioExportRequested: false,
   isSongSidebarOpen: false,
-  isLoopEnabled: createDefaultLoop().isLoopEnabled,
-  loopStartTick: createDefaultLoop().startTick,
-  loopEndTick: createDefaultLoop().endTick,
+  isLoopEnabled: false,
+  loopStartTick: 0,
+  loopEndTick: 0,
 };
 
 export const singingStore = createPartialStore<SingingStoreTypes>({