To eliminate or suppress a decrease in heating capability due to frost formation by delaying the progress of frost formation on an outdoor heat exchanger in a heat pump vehicle air conditioning device. A controller executes a heating mode for causing a refrigerant discharged from a compressor (2) to radiate heat in a radiator (4), reducing the pressure of the refrigerant that has radiated the heat, and absorbing the heart in an outdoor heat exchanger (7), and on the basis of a difference (Delta TXO=(TXObase-TXO)) between the refrigerant evaporation temperature (TXObase) of the outdoor heat exchanger (7) when no frost is formed and the refrigerant evaporation temperature (TXO) of the outdoor heat exchanger (7), corrects a target supercooling degree (TGSC) that is the target value of the supercooling degree of the refrigerant in the radiator (4) such that the target supercooling degree rises as the difference (Delta TXO) increases.