A system software unit performs a first authentication operation with an external device using a first key that is registered in advance. A secure software unit determines whether or not system software satisfies a soundness condition. A dedicated memory unit is used to store a second key. While performing a reregistration operation for reregistering the first key, a system software unit requests the secure software unit to read the second key. When the system software satisfies the soundness condition, the secure software unit generates verification data using the second key. When a second authentication operation performed with the external device using the verification data is successful, the system software unit performs the reregistration operation.