PURPOSE: To aim at the promotion of an energy-saving bid, by controlling the whole operation region of an air mix damper driving device in a way of making a compressor into a state of stoppage at the heating side, while keeping an air mix damper opened in full at the air cooling side.

CONSTITUTION: A controller 50 inputs the signals of a potentiometer 58, a room temperature setter 28, and indoor/outdoor air sensors 29 and 30 all interlocked with a driving device 51 for an air mix damper 4 and, when room temperature changes, turns an electric motor 53 round to the heating side in a counterclockwise direction or to the air cooling side in a clockwise direction, then performs temperature control by operating the air mix damper 4 if a (c) point of a cam 54 exists just between (a) and (b). And, when the cam's C point shifts farther to the air cooling side than an intermediate point (b) that dispenses with both the air cooling and heating, the air mix damper 4 is held in a state of having a heater 3 side fully closed by action of a groove 55 and controls the on-off operation of a compressor 6. Thus not only a bid for energy-saving can be promoted but also the controllability is much improvable.