A vehicle air conditioner which improves the frost formation judging precision of an outdoor heat exchanger, acquires the heating performance, and avoids unnecessary defrosting. A controller executes a heating mode. The controller (32) judges frost formation onto the outdoor heat exchanger (7) on the basis of a refrigerant evaporation pressure PXO of the outdoor heat exchanger (7) and a refrigerant evaporation pressure PXObase of the outdoor heat exchanger (7) during non-frost formation or on the basis of a refrigerant evaporation temperature TXO of the outdoor heat exchanger (7) and a refrigerant evaporation temperature TXObase of the outdoor heat exchanger (7) during the non-frost formation, and allows a high-temperature refrigerant gas to flow through the outdoor heat exchanger (7), thereby performing defrosting of the outdoor heat exchanger (7).