A method of correcting a flare comprising: calculating a distribution of a flare value corresponding to pattern data on the pattern data as a flare map; calculating an occupancy of a pattern having a predetermined flare value on the pattern data as a flare value occupancy for each flare value, by using the flare map; determining a reference flare value to be a reference of the flare value based on the distribution of the flare value occupancy; and performing a pattern correction corresponding to the flare value with a pattern correction amount at the reference flare value as a reference.