A position detection apparatus includes an imaging system, an illumination system including a rotary table having first and second aperture stops, both of which can be positioned on the pupil plane of the illumination system, a first image sensor that detects the image of the mark formed by the imaging system, a second image sensor that senses an image of the aperture stop for the imaging system and that of the first aperture stop, and a controller. The controller corrects the first aperture stop so as to reduce the adverse influence of a displacement of the first aperture stop, based on sensed images of the aperture stop for the imaging system and the first aperture stop. Based on the detected position of the image of the mark, the apparatus detects the position of an object to be detected using the illumination light having passed through the corrected first aperture stop.