When it is assumed that a vehicle is stopped or parked after its engine was stopped and a predetermined period of time has passed, a cold wind side air mixing door, hot wind side air mixing door, cold wind door and rear cold wind side air mixing door are totally closed and a blower is operated for a predetermined period of time. Accordingly, while a cooler is being dried, drying air containing much offensive smell components, which has passed through the cooler, is discharged outside the vehicle. Therefore, it is unnecessary to provide an exclusively used air passage and an opening and closing door for opening and closing the air passage used for composing an air blowing passage to dry the cooler. By utilizing the existing equipment, air used for drying, which has passed through the cooler, containing much offensive smell components can be discharged outside the vehicle.