A pattern data generation method of an aspect of the present invention, the method includes creating at least one modification guide to modify a modification target point contained in pattern data, evaluating the modification guides on the basis of an evaluation item, the evaluation item being a change in the shape of the pattern data for the modification target point caused by the modification based on the modification guides or a change in electric characteristics of a pattern formed in accordance with the pattern data, selecting a predetermined modification guide from among the modification guides on the basis of the evaluation result of the modification guides, and modifying the modification target point in accordance with the selected modification guide.