A casing, which receives a fan, has a suction port forming portion that forms a suction port. A separation tube has a tube upper end portion, which forms an air inlet, through which the air flows into an inside of the separation tube. The tube upper end portion is located on one side of the suction port forming portion in an axial direction such that the tube upper end portion overlaps with a portion of the suction port in the axial direction. A rib is formed at a periphery of the suction port. The periphery of the suction port has: an overlapping region, which overlaps with the tube upper end portion in the axial direction; and a non-overlapping region, which does not overlap with the tube upper end portion in the axial direction. The rib occupies more area in the non-overlapping region than in the overlapping region.