PURPOSE: To increase the response speed of a control system by changing the gains of a blow-off temperature control loop with the velocity of air generated by a blower in the titled device suitable for the control of a blow-off air temperature.

CONSTITUTION: An output from a sensor 5 detecting the blow-off temperature of air and a set-value signal of the blow-off temperature by a temperature setter 7 are compared in a control circuit 6 in a car air conditioner, and an A/M door (an air mix door) 4 is controlled by the deviation signal. The control circuit 6 is changed over by an operational amplifier OP, resistors R2WR4 setting gain distribution in case of arithmetical operation and switches S1WS3 at that time. The circuit is constituted by capacitors C1WC3 forming round loop gains and an A/M door drive circuit 8. Said switches S1WS3 are brought selectively to conductive states by changing over winding RL1WRL3 by a fan switch FS.