1. A pattern correction apparatus for performing both of optical proximity effect correction and process proximity effect correction with regard to a design pattern, comprising: correction calculation means configured to perform correction calculation by two-dimensional model-based optical proximity effect correction for each of sampling points set on pattern edges which form the design pattern; said correction calculation means performing the correction calculation which involves weighting with a two-dimensional distribution of the pattern edges around the sampling point taken into consideration; said weighting being performed such that a high weight is applied to a region in which reaction products which can have an influence on the sampling point are produced but a low weight is applied to any other region.