PURPOSE: To utilize a large amount of heat, which is generated when air is compressed, as power required for operation of a humidifier without wasting the heat for reducing the power consumption by providing a refrigerant heater by which compression heat of a compressor is recovered.

CONSTITUTION: High temperature air compressed and delivered by an unlubricated single stage screw compressor 3 driven by a motor 1 is immediately led to a heater 6 of an absorption type refrigerating machine as a heat source. After passing through the heater 6, the air passes through an after cooler 4 and a gas-water separator 5, which are conventional equipment as an air compressing apparatus, and cooled down to remove moisture. After that, the air is cooled further by an evaporator 8 of the absorption type refrigerating machine, and the water produced there is removed by a gas-water separator 12 to dry the air. On the other hand, the refrigerant evaporates in the heater 6 and flows into a condenser 7 is which refrigerant is cooled and liquefied. Then, the liquid refrigerant absorbs heat in the evaporator 8 and cools the delivery air. On the other hand, the lean solution, which becomes low in the concentration of the refrigerant, is sent to an absorber 11 after passing through the heater 6 and a heat exchanger 9, absorbs the refrigerant coming from the evaporator 8, and is returned to the heater 6 by a pump 10.