The invention discloses a reading device, a control method, and a terminal device, which are capable of improving operability and shortening reading time of commodity information, and further improving reading rate of commodity information. The reading device (10) includes: an opening/closing cover (12) for opening and closing an opening (11a) serving as an entrance and exit of a product, and a housing portion (11) for storing commodities therein, and an RFID antenna for communicating with RFID tags by emitting radio waves, and an opening and closing state acquisition unit obtaining opening and closing states of the opening/closing cover (12), and a reading control portion which changes a communication range between the RFID antenna and the RFID tag when a commodity is stored in the housing portion (11) and the open/close state is changed from an open state to a closed state, and reads commodity information from the RFID tag of each commodity.