The invention prevents the temperature of supplied air from being decreased by a defrosting operation when a vehicle is in operation. During the heating operation, it is judged whether the vehicle is in operation. When the vehicle is in operation, it is judged whether an external heat exchanger is frosted or not relying upon the external air temperature, temperature of the external heat exchanger (coolant) and the time of heating operation. When it is judged that frost is formed, the rotational speed of the compressor is increased to increase the ability to supplying the coolant, to maintain heating ability and to prevent the drop of temperature of the supplied air. When the frost is formed after the operation of the vehicle has been finished, it is judged whether the secondary batteries are being charged or not, i.e., whether the charging circuit of the secondary batteries is connected to the external power source for charging or not. When it has not been connected, the device waits until it is connected, and the defrosting operation is executed at a moment when the charging circuit is connected.