An air filter (30) intermittently rotates by a predetermined rotation angle at each time, while being in contact with a bristle portion (51b) of a rotating brush (51). Accordingly, dust on the air filter (30) is scraped by the bristle portion (51b). The brush member (51) rotates about an axial center of a shaft (51a) at each stop of the intermittent rotation of the air filter (30), to come into contact with a cleaning brush member (52). According, dust on the brush member (51) is removed by the cleaning brush member (52).