A dehumidifying method, using a desiccant wheel having an adsorption surface which is capable of alternately entering a supply air chamber and a regeneration air chamber disposed next to each other, for adsorbing water vapor in supply air flowing through the supply air chamber on the adsorption surface and desorbing the water vapor adsorbed on the adsorption surface with regeneration air flowing through the regeneration air chamber , the method comprising: a dehumidifying step of bringing the supply air into contact with the adsorption surface of the desiccant wheel and causing the desiccant wheel to adsorb the water vapor in the supply air; a cooling step of cooling the supply air dehumidified in the dehumidifying step; a first temperature increasing step of increasing a temperature of the supply air cooled in the cooling step with a temperature increasing medium to reduce a relative humidity of the supply air; a supplying step of supplying an air conditioning chamber with the supply air having the relative humidity reduced in the first temperature increasing step; a second temperature increasing step of increasing a temperature of the regeneration air to reduce a relative humidity of the regeneration air; and a desorbing step of bringing the regeneration air heated in the second temperature increasing step into contact with the adsorption surface and desorbing the water vapor adsorbed on the adsorption surface from the adsorption surface , characterized in that : the cooling step is carried out with an air cooler constituting a part of a heat pump device ; that, the second temperature increasing step is carried out with an air heater constituting a part of the heat pump device ; and that the temperature increasing medium is one of the followings: at least a part of the regeneration air after desorbing the water vapor from the desiccant wheel in the desorbing step; and outside air (OA) or return air (RA) discharged from the air conditioning chamber . a dehumidifying step of bringing the supply air into contact with the adsorption surface of the desiccant wheel and causing the desiccant wheel to adsorb the water vapor in the supply air; a cooling step of cooling the supply air dehumidified in the dehumidifying step; a first temperature increasing step of increasing a temperature of the supply air cooled in the cooling step with a temperature increasing medium to reduce a relative humidity of the supply air; a supplying step of supplying an air conditioning chamber with the supply air having the relative humidity reduced in the first temperature increasing step; a second temperature increasing step of increasing a temperature of the regeneration air to reduce a relative humidity of the regeneration air; and a desorbing step of bringing the regeneration air heated in the second temperature increasing step into contact with the adsorption surface and desorbing the water vapor adsorbed on the adsorption surface from the adsorption surface , the cooling step is carried out with an air cooler constituting a part of a heat pump device ; that, the second temperature increasing step is carried out with an air heater constituting a part of the heat pump device ; and that the temperature increasing medium is one of the followings: at least a part of the regeneration air after desorbing the water vapor from the desiccant wheel in the desorbing step; and outside air (OA) or return air (RA) discharged from the air conditioning chamber . at least a part of the regeneration air after desorbing the water vapor from the desiccant wheel in the desorbing step; and outside air (OA) or return air (RA) discharged from the air conditioning chamber . <EOS>