In a vehicular air conditioner in which a cooling operation and a heating operation are switched by switching a four-way valve, a pressure accumulator is provided in which a coolant, which is related to an aspiration pressure of a compressor, is accumulated when the compressor is operated, and a differential pressure, which is required for switching the four-way valve, between piston rooms is maintained, and the differential pressure, which is required for switching the four-way valve, is generated between the piston rooms of the four-way valve even after the compressor is stopped.