According to one embodiment, a pattern data generating apparatus comprises a storage unit that stores a table defining direct self assembly information that combines a direct self assembly material, a film thickness of the direct self assembly material, and a process condition for the direct self assembly material according to a pattern dimension, a division unit that divides layout data of a device based on the pattern dimension to generate divided layouts, an extraction unit that extracts the direct self assembly information corresponding to the pattern dimension of the divided layout from the table, and a generation unit that generates pattern data by allocating the direct self assembly information extracted by the extraction unit to the divided layouts.