To provide a grinding simulation method for producing a shape with high accuracy even if a range of projections existing on the surface of a workpiece is larger than the irradiation area of an ion beam.

On the basis of the surface shape of a workpiece measured by a measuring instrument and a design shape preliminarily inputted as a design target, the grinding simulation apparatus calculates a removal quantity for removing the surface of the workpiece required for machining the surface shape into the design shape, obtains a relation between the irradiation dosage of an ion beam and the removal quantity of an object to be irradiated which is composed of the same material as the workpiece to be removed by ion beam irradiation, and on the basis of the relation obtained and the profile of the ion beam, grinding/irradiation conditions are determined for the purpose of machining the surface shape into the design shape.