A blower includes: an outside/inside air box into which outside air and inside air are introduced; an impeller to suck and blow out air introduced into the air box; a casing having a bell mouth that forms an air suction port to the impeller, the casing forming a ventilation passage on an outer side of the impeller in a radial direction; and a plate-shaped member provided with a predetermined gap relative to the casing and the bell mouth. A gap passage is defined between the casing and the plate-shaped member. A guide rib is provided at a part of the gap passage opposite to an opening through which air flows into the gap passage. The guide rib guides air flowing through the gap passage in a circumferential direction of the bell mouth.