PURPOSE: To achieve operating state easily in a short time at re-starting, by providing a memory having a backup area and writing in the content of the backup area to other memory at re-start after system down.

CONSTITUTION: After a cause to system down is eliminated, the system is restarted and initialized. Then a restoration section 6 is operated, and the content of a backup area 3A of a memory 3 is written in a memory 2. Thus, the memory 2 is restored to the content before system down. After the restoration, access sections 4aW4n access the memory 2 for various processings and the processing is made continuously from the state before system down.