A projection exposure apparatus which can perform superior observation or projection of a selected mark when the mark is observed or projected through a projection optical system in which a pupil filter is set. The projection exposure apparatus which projects a pattern on a mask through a projection optical system onto a photosensitive substrate held on a substrate stage movable in a plane perpendicular to the optical axis of the projection optical system and which has a pupil filter (optical correction plate) placed on or near the pupil plane of the projection optical system, a reference mark formed on the substrate stage in a scale factor according to the shape of the pupil filter, illuminating means for illuminating the reference mark with illumination light, and light-receiving means for receiving the illumination light having emerged from the reference mark and thereafter having passed the projection optical system.