When a self-cleaning method for an aligner is carried out, a reflecting plate having a convex lens portion is set in an original plate holder, and exposure light rays are irradiated from a light source. The surface of the lens portion is coated with a reflective film. The light rays are reflected by the reflecting plate, diffused, and emitted onto the surface of a condenser lens, thereby breaking down and removing contaminants that are adhered to the surface of the condenser lens. The light rays also enter the interior of the condenser lens to clean away contaminants that are adhered to locations other than a normal exposure path. When a concave mirror and/or a reflecting plate having 50% transmittance is used as the reflecting plate, the emission range of the light rays (i.e., the locations that are cleaned) can be changed.