According to an embodiment, a pattern data generation method is provided. In the pattern data generation method, when a resist on a substrate is exposed using a mask, an optical image at a designated resist film thickness position is calculated using a mask pattern. Feature quantity related to a shape of a resist pattern at the resist film thickness position is extracted, based on the optical image. Also, whether the resist pattern is failed is determined, based on the feature quantity, and pattern data of a mask pattern determined as failed is corrected.