diff --git a/hts/OrderChecker.py b/hts/OrderChecker.py
index 8661a38..67d319b 100644
--- a/hts/OrderChecker.py
+++ b/hts/OrderChecker.py
@@ -31,7 +31,7 @@ class OrderChecker:
 
     def exist(self, ymd, stock_code, mins=30):
         order_df = self.read(ymd)
-        if order_df != None and len(order_df)>0:
+        if order_df is not None and len(order_df)>0:
             tmp = order_df.loc[order_df["stock_code"] == stock_code]
             now = datetime.now() - timedelta(minutes=mins)
             tmp = tmp.loc[now < tmp["datetime"]]