Heat pump type air conditioner for a vehicle in which a noise generated in opening an opening/closing valve (a solenoid valve) during changing of an operation mode is eliminated or reduced. The air conditioner has a dehumidifying and heating mode to let a refrigerant radiate heat in a radiator 4, decompress the refrigerant, and let the refrigerant absorb heat in heat absorber 9 and outdoor heat exchanger 7, and a cooling mode to let the refrigerant radiate heat in the outdoor heat exchanger, decompress the refrigerant, and let the refrigerant absorb heat in the heat absorber. Solenoid valve 21 and solenoid valve 22 opened in the dehumidifying and heating mode. When changing an operation mode from the cooling mode to the dehumidifying and heating mode, a difference between a pressure before each solenoid valve and a pressure after the valve is reduced, and then these valves are opened.