diff --git a/reactionbot.py b/reactionbot.py
index 8039c77..b427e7d 100644
--- a/reactionbot.py
+++ b/reactionbot.py
@@ -42,7 +42,7 @@
     logger = logging.getLogger(logger_name)
     logger.setLevel(logging.INFO)
     log_filepath = LOGS_DIR.joinpath(logger_name + '.log')
-    handler = logging.FileHandler(log_filepath, mode='w')
+    handler = logging.FileHandler(log_filepath)
     handler.setFormatter(formatter)
     logger.addHandler(handler)
     logger.warning('Start reaction bot.')