An air conditioner for vehicles that prevents icing and lack of visibility from developing on window glass of a vehicle during heating, and which permits a dehumidifying operation to be made without lowering of the air blowing temperature. The air conditioner is of a heat pump type comprising a compressor, an exterior heat exchanger, and a first interior heat exchanger, which are provided together with a second interior heat exchanger used as a heat radiator at least during heating. Further, piping lines are provided for introducing a refrigerant gas for passage through the second interior heat exchanger to the exterior heat exchanger through an expansion means, and for introducing the refrigerant gas for passage through the second interior heat exchanger to the first interior heat exchanger through a first expansion means. Thus, dehumidification in the vehicle can be simultaneously performed during heating by respectively performing a heat radiating operation at the second interior heat exchanger and a heat absorbing operation at the first interior heat exchanger.