Illuminating light at a pupil plane of an illumination optical system for illuminating a position detection mark on a substrate is limited to an annular area centered at an optical axis, and a member substantially blocks an image-forming light beam distributed over an area on a pupil plane of an image-forming optical system for forming an image of the position detection mark on an imaging device by receiving light generated from the mark, the area being in image-forming relation to the annular area on the pupil plane of the illumination optical system. Alternatively, a member gives a phase difference of approximately .pi./2 �rad! between the image-forming light beam distributed over the area which is in image-forming relation to the annular area on the pupil plane of the illumination optical system and the image-forming light beam distributed over the area other than that area.