In the disk array system, in the basic chassis, HDD modules are installed from a front surface in a front part of a backboard, and duplex CTL modules are installed up and down from a rear surface in a rear part, and duplex power source modules containing fans are installed in the left and right sides thereof. By the operation of the fans, in the rear part, the cooling air flows separately into each CTL module and into each power source module, and the cooling air having passed through the area of the duct by a block in the CTL module is drawn by the fans in the power source module through a ventilation hole and is then exhausted outside. The cooling air flow path to the plurality of ICs is divided by the block. The rotation speed of the fans is controlled by using a temperature sensor.