Abstract: A dehumidifier comprises a suction unit 45 which humid air 47 is sucked in, a dehumidifying unit 43 having a chiller 56 and for cooling down the humid air sucked in and for dehumidifying by condensing the moisture in the humid air, a discharge unit 46 having a heat radiator 54 and for heating and discharging dry air 49 as dehumidified at the dehumidifying unit, a refrigerant circulating system 44 for cooling down the humid air at the dehumidifying unit and for heating the dry air at the discharge unit, and a heat exchanger 1 for performing heat exchange between the humid air and the dry air as dehumidified at the dehumidifying unit.