In a disk array system, cooling means with a great versatility capable of efficiently performing a cooling and a heat radiation of the objects to be cooled on the circuit board in a small space and a structure capable of stably supplying the power from a DC-DC converter to the electronic components on the circuit board are provided. A circuit board is stored in a logic box in a state where a heat sink is fitted thereto, a power supply section supplies a voltage to the circuit board, and a fan is used in the ventilation for the circuit board. The circuit board has an LSI and a wiring area as the objects to be cooled. A heat sink including a base part having a flat surface to cover the whole of the objects to be cooled and radiator fins is provided. The board fitted with the heat sink is assembled in such a manner. That is, the circuit board and the heat sink are made opposed to each other and then connected with interposing the block with high thermal conductivity, which is filled depending on the height of the objects to be cooled, therebetween. Thereafter, the whole is fixed by the screws and the like.