The present invention is equipped with a plurality of low-cost middle-capacity hard disks that are combined together to realize a large capacity at the same level as a large-capacity hard disk, and performs power-saving management to minimize the power consumption by the hard disks. At the same time, the present invention eliminates delays for accessing the separate hard disks. For this purpose, the present invention puts any of a plurality of drive devices other than a current access-target drive into a power-saving state, and puts the next access-target drive into a stand-by state from the power-saving state during the access to the current access-target drive, by calculating a remaining time until completion of the access to the current access-target drive.