Aligned disk drives are installed in a disk box nearly taking a rectangular shape. Every two of the disk boxes are paired and accommodated in a rack in a multi-stage form. Each pair of disk boxes are disposed with their exhaust planes opposed to each other with a gap therebetween. An air intake plane of each disk box opposite to the exhaust is disposed on a front or rear side of the rack. A draft path, having front and rear walls formed by gaps between disk boxes and side walls on left and right planes of the rack, is formed in the rack center. Exhaust fans disposed on top of the rack and having air intake ports nearly equivalent in dimension to a section of the draft path suck in air through the intake and exhaust planes and draft path, and exhaust the air outside the rack.