A control part controls a first opening-and-closing part to close either one of a first outside air introduction port and a first inside air introduction port when it is determined that outside air introduced from the first outside air introduction port flows into a passenger compartment through the first inside air introduction port, and controls a second opening-and-closing part to close either one of a second outside air introduction port and a second inside air introduction port when it is determined that outside air introduced from the second outside air introduction port flows into the passenger compartment through the second inside air introduction port.