A humidification device is used in a vehicle air conditioner having a cooler disposed in an air conditioning case. The air conditioning case has a ventilation path leading air into a vehicle compartment. The humidification device has an adsorber that absorbs and desorbs moisture, a blower, a door that opens or closes an air flow path, and a controller. The controller switches the air flow path by controlling the door to set (i) a dehumidification mode in which air cooled by the cooler is led to the adsorber, and moisture in the air is adsorbed by the adsorber or (ii) a humidification mode in which air is led to the adsorber, the moisture is moved from the adsorber to the air to humidify the air, and the humidified air is blown toward an occupant.