A disk array apparatus facilitating the management of dummy boards which are dismounted when logic boards are additionally installed, for example. A storage section for storing dummy boards, which are removed when logic boards are additionally installed, is provided in the disk array casing. The storage section is provided in a place where the dummy boards do not adversely affect the passages of the flow of cooling air in the disk array casing and the work of mounting or dismounting the component parts on the rear side of a platter cover for shielding the logic section where logic boards are accommodated, for example, and the dummy boards are fixed to the storage section with screws.