A humidification device for a vehicle air conditioner includes an adsorber having an adsorbent, an adsorption case configured to provide an accommodating space that accommodates the adsorber and includes a moisture-adsorption space and a moisture-desorption space, a humidification-side guiding portion that guides humidification air humidified by using the moisture desorbed within the moisture-desorption space to a vehicle interior, a moving mechanism that moves at least a part of the adsorbent existing in the moisture-adsorption space of the adsorber to the moisture-desorption space while moving at least a part of the adsorbent existing in the moisture-desorption space of the adsorber to the moisture-adsorption space, and a desorption control unit that executes a desorption operation to desorb moisture adsorbed in the adsorbent when humidification of the vehicle interior is stopped.