PURPOSE: To make sure a duplex processing of data and to prevent the lowering of processing speed by storing and holding the data held in a memory to an external storage means when exceeding the set elapse time.

CONSTITUTION: Elapsed days from the last backup day to the present time is calculated based on the date data from among the present time data obtained by a clock circuit 14 and the date data stored in a backup data area 13a provided in a RAM 13. Based on the calculated elapsed days, whether or not the elapsed days are more than one month from the last backup day is confirmed. With more than one month, the data stored in the RAM 13 is inserted in a floppy disk drive 3 for backing up (duplex processing) in the floppy disk(FD). The date data stored in the backup data area 13a is updated by means of the date data out of the present time data obtained from the clock circuit 14.