A disk array device can carry out battery backup including a destage process of data by a battery mounted in a case body of the disk array device and can enhance instantaneous power failure durability to an instantaneous power failure. A logic box mounts a channel controlling unit, a disk controlling unit, a cache memory and a switch; and a hard disk box mounts a plurality of memory devices. A battery box mounts a nickel hydrogen battery for supplying a backup power source at the time of a power failure and is disposed at a lower portion of each case body including the logic box and the hard disk box. The nickel hydrogen battery of the battery box is cooled through natural convection of air created inside the case body by a fan for cooling each of the logic box and the hard disk box.