A dehumidifying system supplies a gas free of organic substances. The dehumidifying system includes a holding case, and a rotor rotatably held in the holding case and bearing an adsorbent. The interior of the holding case is divided into an adsorbing zone and a regenerating zone by partition plates attached to the holding case. A process gas is supplied into the adsorbing zone. The process gas processed in the adsorbing zone is supplied into an objective space. A regenerating gas is supplied into the regenerating zone to eliminate moisture and organic substances adsorbed by the adsorbent in the adsorbing zone from the adsorbent.