A method includes: generating electron beam exposure data, used for electron beam exposure, from design data of a semiconductor device; extracting differential information indicating a difference in shape between an electron beam exposure pattern formed on a substrate through electron beam exposure on the basis of the electron beam exposure data and a photoexposure pattern formed on the substrate through photoexposure on the basis of the design data of the semiconductor device; determining whether the size of the difference in shape between the electron beam exposure pattern and the photoexposure pattern falls within a predetermined reference value; acquiring shape changed exposure data by changing the shape of the pattern of the electron beam exposure data in accordance with the differential information and updating the electron beam exposure data; and repeating the differential extraction, the determination and the updating when the size of the difference falls outside the predetermined reference value.