Disclosed therein is an air conditioner for a vehicle, which includes an evaporator and a storage tank getting in surface contact with each other, thereby doubling a cold storage effect by directly transferring cold air of the evaporator to the storage tank in a cooling mode, maximizing the cold storage effect because condensate water generated from the surface of the evaporator additionally cools the surface of the storage tank, and effectively enhancing heat-exchanging performance without increasing capacity of the storage tank. The air conditioner further includes heat-exchanging means mounted inside the storage tank so as to enhance the heat exchange performance of a heat carrier more.