Abstract: An alignment device for aligning a reticle and a wafer with the aid of a projection lens system for projecting an integrated circuit pattern of the reticle onto the wafer, wherein a light beam from the wafer is passed throught the projection lens and is directed by way of an objective lens to a spatial filter to detect a positional relation between the reticle and the wafer. According to the position of an optical axis of the objective lens relative to an optical axis of the projection lens and according to the telecentricity of the projection lens, the spatial filter is displaced relative to the optical axis of the objective lens, whereby a particular component of the light beam from the wafer is positively extracted out, without being affected against by displacement of the objective lens for the alignment operation.