Obtaining a function by convoluting a function representing a light intensity distribution formed by an illumination apparatus on a pupil plane of a projection optical system and a pupil function of the projection optical system. Calculating a Fourier transformed function by Fourier transforming the product of the obtained function and a diffracted light distribution from a pattern on an object plane of the projection optical system. Producing data of the pattern of the mask based on the Fourier transformed function.