diff --git a/src/pixiv/pixiv_api.py b/src/pixiv/pixiv_api.py
index 0968774..403d251 100644
--- a/src/pixiv/pixiv_api.py
+++ b/src/pixiv/pixiv_api.py
@@ -9,6 +9,8 @@ import pixivpy3
 
 cpu_count = os.cpu_count()
 max_thread_num = cpu_count * 2 if cpu_count is not None else 4
+if max_thread_num > 10:
+    max_thread_num = 10
 
 
 def dowload_pixiv_images(
@@ -22,6 +24,7 @@ def dowload_pixiv_images(
     json_result = api.illust_detail(illust_id)
     illust = json_result.illust
     if not illust["visible"]:
+        logging.info("Can't be viewed, return None")
         return None
     pages = illust["meta_pages"]
     if len(pages) > 0: