A vehicle air conditioner selectively switches one of a cooling mode in which an interior heat exchanger of a refrigerant cycle is operated as an evaporator for cooling air, and a hot-gas heating mode in which the interior heat exchanger is operated as a radiator for heating air. The cooling mode is selected by turning on an air-conditioning switch, and the hot-gas heating mode is selected by turning on a hot gas switch. When both the switches are turned on at the same time, a control unit determines a priority mode having a higher necessity among the hot-gas heating mode and the cooling mode. Specifically, the hot-gas heating mode is automatically set by the control unit when the outside air temperature is lower than a predetermined temperature, and the cooling mode is automatically set by the control unit when the outside air temperature is higher than the predetermined temperature.