PURPOSE: To decrease a discharge temperature of a compressor and to exclude bad influences exerted on the compressor due to high temperatures in summer season by a method wherein a suction air in the compressor of a compressor device in which a deforgging unit provided with the compressor and a heat exchanger is jointly installed, is cooled by a discharged liquid from the heat exchanger.

CONSTITUTION: The compressor 2 intakes the air through a suction air purifier 5 and a suction air cooler 14 and compresses the air to be discharged. The compressed air discharged is flowed in a secondary flowed heat exchanger 9 to be cooled by a regrigerant gas after being flowed in a primary haet exchanger 8 of a refrigeration type defogging unit 7 through a cooler 6 and precooled, and the moisture in the compressed air is separated at the same time. The low temperature compressed air of which moisture is removed is fed to the suction air cooler 14 to cool the suction air and then supplied as a cooling medium of the primary heat exchanger 8 of the defogging unit 7 and allowed to precool the discharged compressed air of the compressor 2. The compressed air which is precooled in the cooler 14 is decreased in temperature by being heated by contraries and sent out as a dried compressed air.