PURPOSE: To accurately detect abnormality or normalcy of backup data by storing plural preliminarily determined data in a backup memory at the time of turning off a main power source and confirming normalcy by coincidence between plural read data and plural preliminarily determined data at the time of turning on the main power source.

CONSTITUTION: Plural preliminarily determined data are stored in a backup memory 100 by a write means 200 at the time of turning off the main power source. When these plural data read out from the backup memory 100 coincide with plural preliminarily determined data at the time of turning on the main power source, normalcy of the backup memory 100 is confirmed by a discriminating means 400. Thus, abnormality or normalcy of backup data is surely and accurately detected independently of the allowable stand-by voltage of the memory. Since it is unnecessary to check all of backup data and a check data storage area is used for operation processing after turning-on of the main power source, the backup memory 100 is effectively used.