A communications system configured to execute data transmission between a transponder having no radio wave generating source thereof and a reader/writer is provided. The communications system includes, a service permission level notifier configured to tell a service permission level for associated with a received signal level for permitting service acceptance from the reader/writer to the transponder, and an access controller configured to determine in the transponder whether the received signal level from the reader/writer is at the notified service permission level to determine accessibility to the transponder from the reader/writer.