A projecting apparatus for forming an image of a mask on a wafer by a projector of a unit magnification reflection system having a concave spherical mirror and a convex spherical mirror. The distance from the projector to the mask or the upper side of a mask holder for holding the mask and the distance from the projector to the wafer are measured. An error of the image-forming position is computed from the distance measurements. At least one of the mask, the wafer and the projector is moved along the direction of projection in a manner to eliminate the error of the image-forming position computed, thus attaining automatic focus adjustment.