[Problem] To provide a heat pump vehicle air conditioner that implements comfortable heating in a vehicle interior during travel and prolongs traveling distance by preventing or suppressing frost on an exterior heat exchanger when heating the vehicle interior in advance while the vehicle is plugged in. [Solution] This vehicle air conditioner is provided with a heat transfer medium circulation circuit (23) for heating air supplied from an air flow channel (3) to a vehicle interior. A controller has a frost estimation means that estimates frost on an exterior heat exchanger (7). In a heating mode which is implemented when electricity is supplied from an external power source to a compressor (2) or to a battery that supplies power in order to drive the compressor (2), the controller, on the basis of the estimation of the frost estimation means, implements heating by means of the heat transfer medium circulation circuit (23) when frost on the exterior heat exchanger (7) is predicted.