An alignment device includes an image pickup optical system for picking up an image of a first reference mark disposed on a mask and an image of a second reference mark disposed on a photosensitive substrate through an image pickup optical system, a memory for storing information associated with the imaging characteristics of the image pickup optical system, and a correction system for correcting the positions of the first and second reference marks, detected using image information from the image pickup system, on the basis of the information associated with the imaging characteristics of the image pickup optical system.