A control unit (30) controls a first opening/closing unit (34) such that either a first outside air introduction port (36a) or a first inside air introduction port (36b) is brought into a closed state when outside air introduced from the first outside air introduction port is determined to flow out from the first inside air introduction port into a vehicle interior, and controls a second opening/closing unit (35) such that either a second outside air introduction port (37a) or a second inside air introduction port (37b) is brought into a closed state when outside air introduced from the second outside air introduction port is determined to flow out from the second inside air introduction port into the vehicle interior.
