A memory medium stores a program for generating data on an original pattern used in an exposure apparatus forming an image of a target pattern on a substrate, the program comprising a determination step of determining a final assist pattern based on a light intensity distribution formed by a projection optical system when, of a main pattern and an assist pattern to accompany the main pattern which form the original pattern, only the assist pattern is inserted in an object plane of the projection optical system, and a combining step of combining the final assist pattern and the main pattern to generate data on the original pattern, wherein in the determination step, the final assist pattern is determined by repeating a process of calculating and evaluating the light intensity distribution, and a process of changing the assist pattern to be inserted in the object plane of the projection optical system.