diff --git a/main.ipynb b/main.ipynb
index cb7c28a..5506b9a 100644
--- a/main.ipynb
+++ b/main.ipynb
@@ -333,8 +333,9 @@
     "        if len(bought_unit_amounts) > 0:\n",
     "            bought_unit_amount_before = bought_unit_amount\n",
     "\n",
-    "            bought_unit_amount = bought_unit_amounts[0]\n",
-    "            used_jpy *= bought_unit_amount / bought_unit_amount_before\n",
+    "            if bought_unit_amount_before > 0:\n",
+    "                bought_unit_amount = bought_unit_amounts[0]\n",
+    "                used_jpy *= bought_unit_amount / bought_unit_amount_before\n",
     "\n",
     "        now_ticker = pub.get_ticker('eth_jpy')\n",
     "        now_sell_jpy = int(now_ticker.get('buy', '0'))\n",