An exposure apparatus for exposing to a substrate the image of the desired pattern of a mask having a mark and a desired pattern formed thereon. Light source for illuminating the mask by at least part of the laser light from the light source, a projection optical system, movable stage, position detecting for detecting the relative position of the stage and the mask and outputting a position signal, a fiducial member formed integrally with the stage, the fiducial member having a fiducial pattern disposed thereon. A second illuminating optical system for illuminating the fiducial pattern from the opposite side of the projection optical system with respect to the fiducial member. The second illuminating optical system having a plurality of reflecting members for directing at least part of the laser light from the light source to the fiducial pattern. Normalizing a second detection signal on the basis of a first detection signal, and processing for determining the position of the image of the mark formed on the predetermined surface by the projection optical system, on the basis of a position signal and the second normalized detection signal.