A mobile telephone terminal (2) is provided with an electrical field strength measurement unit (201) that receives radio signals from wireless base stations (31) and measures the strengths thereof; a registration destination base station selection unit (206) that selects one of the wireless base stations (31) that sent the received radio signals as a position registration destination; a position registration execution unit (203) that sends a position registration request to the selected wireless base station (31); and an execution timer expiry determination unit (210) that performs a position registration update process by causing, when a predetermined amount of time has elapsed following the position registration, the registration destination base station selection unit (206) to select a wireless base station (31), and causing the position registration execution unit (203) to send a position registration request to the selected wireless base station (31).