Abstract: If there is not a key operation over a predetermined period of time, a lock control unit receives a timeout signal input from a timer. If the housings are closed, the lock control unit receives a detection result indicating that the housings are closed from an open/close detecting unit. If the timeout signal is input, or if the detection result supplied from the open/close detecting unit indicates that the housings are closed, the lock control unit determines that a lock instruction has been issued, and determines whether the state of the portable telephone device satisfies a predetermined condition. If the predetermined condition is satisfied, the lock control unit outputs a key operation lock activation signal to a control unit. If the predetermined condition is not satisfied, the lock control unit waits for the predetermined condition to be satisfied before outputting a key operation lock activation signal.