A method of manufacturing an exposure mask includes generating or preparing flatness variation data relating to a mask blanks substrate to be processed into an exposure mask, the flatness variation data being data relating to change of flatness of the mask blank substrate caused when the mask blank substrate is chucked by a chuck unit of an exposure apparatus, generating position correction data of a pattern to be drawn on the mask blanks substrate based on the flatness variation data such that a mask pattern of the exposure mask comes to a predetermined position in a state that the exposure mask is chucked by the chuck unit, and drawing a pattern on the mask blanks substrate, the drawing the pattern including drawing the pattern with correcting a drawing position of the pattern and inputting drawing data corresponding to the pattern and the position correction data into a drawing apparatus.