A laser beam position sensing arrangement using two similar sensors where, instead of the first sensor being aligned normal to the beam scan path, the angle which bisects the two sensors is aligned normal to the beam scan path. The improved housing can have one or more of the following aspects. With respect to the newly-forming portions, enlarged patterns are formed by an electron beam drawing apparatus to form new master reticles, and reduced images of the newly formed master reticles are exposed while stitching screens using an optical-type projection exposure apparatus.