A method of verifying photomask-pattern-correction results includes steps of cutting away photomask patterns of a region to be subjected to correction, forming photoresist models used for execution of an optical-proximity-effect-correction operation, executing the optical-proximity-effect-correction operation of the photomask patterns with respect to the photoresist models, executing an exposure simulation for simulating photoresist patterns formed on a photoresist film to which the photomask patterns are transferred after the optical-proximity-effect-correction operation, and designating parameters required for executions of the cutting away the photomask patterns of the region, the forming of the photoresist models, the optical-proximity-effect-correction operation, and the exposure simulation.