PURPOSE: To accept a transaction even while backup processing is being performed by sampling backup data from a data base stored in a first data base storage means, and continuing transaction processing by a second data base storage means.

CONSTITUTION: A first disk device 17a is separated from the transaction processing, and redo logs 15a, 15b and undo logs 16a, 16b are started to accumulate in main storage 14a, 14b by a log accumulation means 13. Thence, the backup data is sampled from the data base(DB) 18a on the first disk device 17a, and during that time, the transaction processing is continued by a second disk device 17b. When the sampling of the backup data is completed, the DB 18a on the first disk device 17a is updated by the data of redo log 15a(15b) by a data base restoring means 12, and it is restored to the DB of same content as that of the second disk device 17b at the present time, and the redo logs 15, and the undo logs 16 are deleted, then, processing is completed.