An air conditioner for a vehicle has a heat pump type refrigerant circuit capable of operating at least in a heating mode. The air conditioner comprises a motor fan for supplying air heated by a heat exchanger to the interior of the vehicle during operation of the heating mode, a sensor for detecting the temperature of the air at a position downstream of the heat exchanger and a control unit for controlling the volume of the air supplied by the motor fan to a predetermined minimum volume by controlling the drive of the motor fan when the detected air temperature is lower than a predetermined temperature. Even in a condition where a sufficiently large heat radiation from the heat exchanger cannot be expected, a large volume of cold air that has been insufficiently heated can be prevented from being discharged into the interior of the vehicle. Because the motor fan is driven at a condition of minimum air volume even when the detected temperature is lower than the predetermined temperature, a rapid variation of air volume caused at the time of changing a fan-stopping condition to a fan-driving condition can be avoided and an abnormal increase in the discharge pressure of the heat pump compressor can be prevented.