This invention discloses a position detection method for detecting the focus position of an optical position detection apparatus including an image sensor and an optical system which forms an image of a target object on the image sensing surface of the image sensor. In this method, the relationship between the position of the target object in the optical-axis direction of the optical system and the evaluation value of the signal output from the image sensor is measured, and the position of a peak close to a reference focus position, which is selected if the evaluation value has a plurality of peaks in the measured relationship, is detected as the focus position.