To secure a fine heat radiating action from a plurality of heat exchangers by providing an air passage having an outside air taking in port and an exhaust port and arranging a plurality of heat exchangers in series in the air passage.

An air flowed into an air passage 6 through an outside air taking in port 4 then passes through a condenser 8a and an oil cooler 9a in order, and flows out from an exhaust port 5. The condenser 8a and the oil cooler 9a exchange heat with the air flowing through the the air passage 6 to carry out the heat radiating action of the condenser 8a and the oil cooler 9a. A common air passage 6 is provided for a plurality of heat exchangers, and the heat exchangers are arranged in series inside the air passage 6. Thus the opening areas of an outside air taking in port 4 and of the exhaust port 5 can be smaller, and the air resistance of an aircraft can therefore be made smaller. In addition, since a space necessary for the cooling device can be smaller, the degree of freedom in the case where various devices are loaded in an engine room can be hightened.