The invention simulates polishing amount taking into account pressure concentration that occurs in the vicinity of the edge of a substrate when a small-diameter buffing pad overhangs the substrate to be buffed.One embodiment of the invention provides a method for simulating polishing amount in a case where a polishing pad of a smaller size than a substrate is used to buff the substrate. The method includes measuring distributions of pressure that is applied from the polishing pad to the substrate according to each overhang amount of the polishing pad relative to the substrate by using a pressure sensor, and correcting the pressure that is used in the polishing amount simulation in accordance with the overhang amounts and the measured pressure distributions.