1. A design layout correcting method implemented by a computer, the method comprising: dividing a design layout of a circuit pattern formed in one layer into at least a first mask pattern and a second mask pattern; setting a design pattern corresponding to a pattern defect area of the first mask pattern or the second mask pattern as a correcting target pattern when correcting the first mask pattern or the second mask pattern; setting a correcting target region corresponding to an arrangement position of the correcting target pattern within the first mask pattern or the second mask pattern; setting a verifying region configured to perform verification of the correcting target region within the first mask pattern or the second mask pattern; correcting the correcting target pattern within the correcting target region; and verifying whether or not the first and second mask patterns are a desired design layout within the verifying region.