If the key of the key operation unit is continuously pushed down for not less than 3 minutes in a state in which the pushdown can hardly be considered as a user operation, the control unit distinguishes this pushdown from the long-time key operation and executes the battery saving processes. Even if the pushdown is continued, the control unit turns off the backlight and the key illumination light and stops the key scanning process of reading a key status of the key operation unit as detected by the key controller.