PURPOSE: To improve the regenerating efficiency of adsorbent and to prolong the life of adsorbent by supplying the exhaust air of actuator into a purge storage vessel of compressed air drying unit during the regeneration to effectively utilize the exhaust air.

CONSTITUTION: An air discharge port 112 for exhaust air of an actuator, such as an air-spring 10, is connected through a solenoid valve 30 to each purge storage vessel 42, 52 of a 1st compressed air drying unit 40 and a 2nd compressed air drying unit 50. When the compressed air sent from an air compressor 100 is dehumidified in the 1st compressed air drying unit 40 and the regeneration of adsorbent is carried out in the 2nd compressed air drying unit 50, the inlet 501 of the drying unit 50 is intercepted from the air compressor 100 by a solenoid valve 80 and the outlet 502 is connected with the air-spring 10 through the valve 30. A drain valve 54 is opened by receiving the pressure from an air storage vessel 20, and the compressed air in the purge storage vessel 52 and the discharged air from the air-spring 10 are reversely flowed in the main body part 500 to regenerate the adsorbent.