PURPOSE: To use an inexpensive change-over valve of room temperature specifications by installing a cooler for cooling high temperature air used for desorption between a dehumidifying tower and an inlet side change-over valve in an apparatus in which a process for adsorbing water vapor on an adsorbent and a process for regenerating the adsorbent by drying are changed over alternately.

CONSTITUTION: When air which was cooled and dehumidified by a cooler in a preceding stage is supplied to a dehumidifying tower 1 through an inlet side change-over valve 3, water vapor is adsorbed by an adsorbent 2 to make air dry, and the air is taken out through a check valve. Part of the dry air is sent to a heater 5 through a flow rate meter 6 and heated to be sent to the tower 1a which adsorbed water vapor. The air used for the regeneration of the adsorbent 2 by heat-drying the adsorbent 2 in the tower 1a and removing adsorbed water vapor, after being sent with water vapor, is cooled by a cooler 7 to be discharged in the air through the change-over valve 3. Since the valve 3 is not exposed to high temperature air, an inexpensive solenoid valve of room temperature specifications can be used.