PURPOSE: To decrease the quantity of cooling air to be taken in, and to economize combustion by disposing heat pipes into an introducing pipe to the primary heat exchanger of high-pressure high-temperature air extracted from an engine and a cabin air exhaust pipe and giving the potential heat of high-temperature air to exhausted air.

CONSTITUTION: One part of the potential heat of the high-pressure high-temperature air of the engine 1 is discharged to the exhaust 11 of a cabin 10 through the heat absorbing section 22 andheat radiating section 23 of the heat pipe 21 and the temperature is dropped, and the air flows into the primary heat exchanger 3, and is cooled by cooling air taken in through a valve 14. The air is compressed adiabatically by means of a compressor 5. The potential heat of the air is radiated to the exhaust 11 through the heat absorbing section 26 and heat radiating section 27 of the heat pipe 25, and the air is forwarded to the cabin 10 through a secondary heat exchanger 7, an expander 6 and a mixing chamber 9. Accordingly, the quantity of cooling air being taken in is decreased by dropping the temperature of air flowing into the primary and secondary heat exchangers 3, 7, while the airframe resistance is reduced, and fuel consumption can be economized.