PURPOSE: To improve cooling efficiency and to improve the efficiency of a heat exchanger by a method wherein cold air and hot air are guided in a direction different from that of the intake air flow passages of a receiving part and a radiation part by means of an air guide or a radiation guide.

CONSTITUTION: A cold air flow is guided by an air guide 6 and is fed to a position above an electronic device unit 5 being a substance to be cooled. Simultaneously, in order to take in air in a casing through a suction port 7 with the aid of a fan motor 31, cold air fed to a position above a casing 1 is sucked after the passage of it through a space in the vicinity of the electronic device unit 5 and the internal space thereof, and a cold air flow is circulated from above to below in the casing. The open air the temperature of which is increased resulting from contact with a radiation fin 42 through the blast motion of a radiation fan motor 41 is guided by a radiation guide 8 and discharged in an oblique downward direction outside the casing 1. Since the direction of the open air taken in through a suction port 43 is differed from that of the hot open air guided by the radiation guide 8 for discharge, two different kinds of the open air is prevented from direct mixture with each other.