To provide an air conditioner capable of preventing the deterioration of the amenity of a passenger caused by the change of a conditioned-air supply temperature, and preventing the frosting of an evaporator.

In this air conditioner 1 comprising a compressor 5 for compressing a gaseous refrigerant, a condenser 6 for condensing the gas refrigerant of high pressure by exchanging heat with the outside air, and an expansion valve 7 for changing a liquid refrigerant of a high temperature and high pressure to a liquid refrigerant of a low temperature and low pressure, and further comprising a refrigerating cycle 2 for supplying the liquid refrigerant of the low temperature and the low pressure to the evaporator 4, a motor 8 for driving the compressor 5, and a rotational frequency control means 11 for controlling the rotational frequency of the motor 8, the rotational frequency control means 11 controls the rotational frequency of the motor 8 on the basis of the pressure at the low pressure-side of the refrigerating cycle 2.