A position detector (16), configured to detect a position of a mark on an object to be detected, comprises an image pickup unit (34), an optical system, a noise obtaining unit (36) and a correction unit (38). The image pickup unit picks up an image of the object to be detected. The optical system forms an image of the object to be detected on an image pickup surface of the image pickup unit. The noise obtaining unit obtains noise information by picking up an image of a region other than the mark using the optical system and the image pickup unit in accordance with the result of adjustment of an optical member included in the optical system. The correction unit corrects, using the noise information obtained by the noise obtaining unit, the image of the mark obtained using the optical system and the image pickup unit.