A commodity container includes a main body with a container space and a radio frequency reader with a communication range that covers an opening of the container space. The radio frequency reader outputs tag information based on a radio frequency signal from a wireless tag and outputs time variation information indicating a time variation of the radio frequency signal. A registration device is attached to the main body and includes a communication interface to receive the tag and time variation information, and a processor configured to determine a time variation in a positional relationship of the wireless tag and the radio frequency reader based on the time variation information and update a commodity registration list based on the determined time variation of the positional relationship.