Time elapsed from the time when the sensor cover is opened and power supply to the fingerprint sensor is turned from off to on is counted and when there is no fingerprint image read-in command within a specified period of time power supply to the fingerprint sensor is turned off. Even if power supply to the fingerprint sensor is turned off, when a fingerprint image read-in command executes power supply to the fingerprint sensor is turned on and read-in of a fingerprint image commences. If a fingerprint image read-in command executes when the sensor cover is closed, that command is invalidated. In such a configuration, the opening and closing of a sensor cover works in synchronicity with on/off control of power supply for a fingerprint sensor and even when the sensor cover is open, wasteful electricity consumption through power supply continuing if the fingerprint sensor is not used within a specified period of time is prevented.