During a normal update process, a password transmitted from a personal computer is compared with password already stored in a flash memory. When the passwords match, a transmitted program is written over the stored program. When a change mode is set by a user, the transmitted password is not compared with the stored password. The transmitted program is written over the stored program. Alternatively, even when the two passwords are compared and the, two passwords do not match, if the change mode is being set, the transmitted program is written over the stored program. Accordingly, during the change mode, regardless of whether or not the transmitted password matches the stored password, the transmitted program is written over the stored program.