1. A non-transitory computer-readable storage medium comprising a mask pattern correction program for correcting a design pattern which serves as a source to form a mask pattern so that, by exposure of a mask with a pattern formed thereon onto a substrate, the mask pattern is transferred as designed, the mask pattern correction program, when executed by a computer, causes the computer to perform; the steps of: determining, before simulation of a dimension of the pattern transferred by exposure, whether a simulation result will converge; and classifying design pattern edges into first and second target edges, correct the first target edges and perform simulation thereon if it is determined that the simulation result will not converge.