An origin of a reference coordinate system is assigned to one of a plurality of center points, and center point coordinates according to the reference coordinate system are assigned to remaining center points, so that reference marks successively correspond to center points of a plurality of microscopes fixed to a base. Beam position detection marks disposed between the reference marks with exposure points of exposure heads fixed to the base are crossed to assign beam coordinates according to the reference coordinate system to the exposure points. Thus, alignment may be easily and accurately performed, and is effective for increasingly larger apparatuses.