In view of realizing a lithographic process which makes it possible to estimate and correct flare with an extremely high accuracy, and causes only an extremely small dimensional variation in width, over the entire portion not only of a single shot region, but also of a single chip region, a mask pattern correction device of the present invention has a numerical aperture calculation unit calculating, for every single shot region, flare energy for a mask pattern corresponding to a transferred pattern, based on an exposure layout of a plurality of shot regions, or more specifically, while considering flare from a plurality of shot regions located around every single shot region.