A centrifugal fan has a circular main plate driven and rotated by a motor rotary shaft, a plurality of blades fixed to an outer circumferential portion of the main plate and spaced apart at predetermined intervals in a circumferential direction of the main plate, and a side plate attached to ends of the blades opposite to the main plate. An air inlet port is formed at the center of the side plate. The side plate inclines outward in centrifugal directions from the air inlet port and has an arcuate cross section with a predetermined radius of curvature. A dead water region reducing space is formed between the blades and the side plate. The dead water region reducing space forms a smooth flow between the two surfaces of each blade, bringing about desirable blade performance.