Air conditioner for a vehicle in which low pressure protection is accurately performed to improve reliability. A controller adjusts a number of revolution Nc of a compressor 2 so that a detected value does not decrease below a limiting target value TGTs, on the basis of the detected value of a suction temperature sensor and a limiting target value TGTs set to a suction refrigerant temperature of the compressor 2. The controller has a predetermined limiting lower limit TGTsL and a predetermined limiting upper limit TGTsH which is higher than the predetermined limiting lower limit, and adjusts the number of revolution Nc of compressor 2 so that the limiting target value TGTs is the limiting upper limit TGTsH on startup of compressor 2, and the controller gradually decreases the limiting target value TGTs toward the limiting lower limit TGTsL, when the detected value decreases to the limiting upper limit TGTsH.