A disk array system includes a plurality of disk drives and at least one unit box including the plurality of disk drives aligned in the thickness direction of the disk drive, each disk drive including a thin case accommodating a recording disk, a read/write head, and a driving mechanism for driving the recording disk and the read/write head, and a control board for controlling the driving mechanism, the control board being mounted on the thin case. In the disk array system, the thin case and the unit box are composed of a thermally-conductive material, the unit box includes surfaces parallel to the thickness direction of the plurality of disk drives, and at least one of the surfaces has a cold plate filled with a refrigerant. Heat generated at the disk drives is transferred to the cold plate, thereby improving cooling performance.