A method of determining a pattern of a mask to be used in an exposure apparatus. The mask is arranged on an object plane of a projection optical system. The method includes calculating a value of a first evaluation function used to evaluate a cost of drawing a provisional pattern on a mask blank to manufacture the mask, calculating a value of a second evaluation function used to evaluate an image of the provisional pattern, which is formed on an image plane of the projection optical system when a mask having the provisional pattern is arranged on the object plane, and changing the provisional pattern. The calculations are repeated, and the provisional pattern is determined as the pattern of the mask, when the value of the first evaluation function meets a first predetermined standard and the value of the second evaluation function meets a second predetermined standard.