diff --git a/hokaku.js b/hokaku.js
new file mode 100644
index 0000000..bdb7818
--- /dev/null
+++ b/hokaku.js
@@ -0,0 +1,190 @@
+(() => {
+  'use strict';
+
+  document.addEventListener("DOMContentLoaded", () => {
+
+    // =========================
+    // 定数
+    // =========================
+    const START_POS = [38.891, 139.824];
+    const CAPTURE_DISTANCE = 30; // m
+    const NEAR_DISTANCE = 100;   // m
+    const CAPTURE_RATE = 0.7;    // 捕獲成功率
+
+    // =========================
+    // DOM
+    // =========================
+    const titleEl = document.getElementById("title");
+    const startBtn = document.getElementById("start");
+    const stopBtn = document.getElementById("stop");
+    const captureBtn = document.getElementById("capture");
+
+    // =========================
+    // 状態
+    // =========================
+    let map;
+    let playerMarker;
+    let monsterMarker = null;
+    let monsterLatLng = null;
+
+    let watchId = null;
+    let nTrial = 100;
+    let canCapture = false;
+
+    // =========================
+    // Map 初期化
+    // =========================
+    function initMap() {
+      map = L.map("locationmap", { tap: true })
+        .setView(START_POS, 16);
+
+      L.tileLayer("https://{s}.tile.osm.org/{z}/{x}/{y}.png", {
+        attribution:
+          '&copy; <a href="http://osm.org/copyright">OpenStreetMap</a> contributors'
+      }).addTo(map);
+
+      playerMarker = L.marker(map.getCenter()).addTo(map);
+      playerMarker.bindPopup("STARTを押して探索開始").openPopup();
+    }
+
+    // =========================
+    // モンスター生成
+    // =========================
+    function spawnMonster(center) {
+      const offsetLat = (Math.random() - 0.5) * 0.002;
+      const offsetLng = (Math.random() - 0.5) * 0.002;
+
+      monsterLatLng = L.latLng(
+        center.lat + offsetLat,
+        center.lng + offsetLng
+      );
+
+      if (monsterMarker) {
+        map.removeLayer(monsterMarker);
+      }
+
+      monsterMarker = L.marker(monsterLatLng, {
+        title: "なにかの気配"
+      }).addTo(map);
+    }
+
+    // =========================
+    // 位置更新
+    // =========================
+    function updateLocation(latlng) {
+      map.panTo(latlng);
+      playerMarker.setLatLng(latlng);
+
+      if (!monsterLatLng) {
+        spawnMonster(latlng);
+      }
+
+      const distance = map.distance(latlng, monsterLatLng);
+      let message = "探索中…";
+
+      if (distance < CAPTURE_DISTANCE) {
+        message = "🎯 モンスターが近い！捕獲できる！";
+        canCapture = true;
+        captureBtn.disabled = false;
+      } else if (distance < NEAR_DISTANCE) {
+        message = "👀 気配が近い…";
+        canCapture = false;
+        captureBtn.disabled = true;
+      } else {
+        canCapture = false;
+        captureBtn.disabled = true;
+      }
+
+      playerMarker.setPopupContent(message).openPopup();
+    }
+
+    // =========================
+    // 捕獲処理（ガチャ）
+    // =========================
+    function captureMonster() {
+      if (!canCapture || !monsterLatLng) return;
+
+      const success = Math.random() < CAPTURE_RATE;
+
+      if (success) {
+        playerMarker.setPopupContent("🎉 捕獲成功！").openPopup();
+      } else {
+        playerMarker.setPopupContent("💨 逃げられた…").openPopup();
+      }
+
+      if (monsterMarker) {
+        map.removeLayer(monsterMarker);
+      }
+
+      monsterMarker = null;
+      monsterLatLng = null;
+      canCapture = false;
+      captureBtn.disabled = true;
+    }
+
+    // =========================
+    // GPS 成功
+    // =========================
+    function onSuccess(pos) {
+      const latlng = L.latLng(
+        pos.coords.latitude,
+        pos.coords.longitude
+      );
+      updateLocation(latlng);
+    }
+
+    // =========================
+    // GPS エラー
+    // =========================
+    function onError() {
+      nTrial--;
+      playerMarker
+        .setPopupContent(`捕捉失敗… 残り ${nTrial} 回`)
+        .openPopup();
+
+      if (nTrial <= 0 && watchId !== null) {
+        navigator.geolocation.clearWatch(watchId);
+        watchId = null;
+        titleEl.textContent = "ERROR";
+      }
+    }
+
+    // =========================
+    // 追跡制御
+    // =========================
+    function startWatch() {
+      stopWatch();
+      watchId = navigator.geolocation.watchPosition(
+        onSuccess,
+        onError,
+        { maximumAge: 0, timeout: 3000, enableHighAccuracy: true }
+      );
+      titleEl.textContent = "探索中";
+    }
+
+    function stopWatch() {
+      if (watchId !== null) {
+        navigator.geolocation.clearWatch(watchId);
+        watchId = null;
+        titleEl.textContent = "STOP";
+        playerMarker.setPopupContent("探索を停止しました").openPopup();
+      }
+    }
+
+    // =========================
+    // イベント
+    // =========================
+    startBtn.addEventListener("click", startWatch);
+    stopBtn.addEventListener("click", stopWatch);
+    captureBtn.addEventListener("click", captureMonster);
+
+    // マップクリック（デバッグ用）
+    map?.on?.("click", () => {});
+
+    // =========================
+    // 起動
+    // =========================
+    initMap();
+
+  });
+})();