To easily obtain polyhedral having an error of an arbitrary physical quantity within a tolerance without excessive precision.

A polyhedron generation means 1b generates a plurality of sample polyhedral data having meshes corresponding in number to sampling meshes. An error calculation means 1d calculates an error between an object shown by three-dimensional CAD data and a polyhedron shown by sample polyhedral data for each of the sample polyhedral data, in relation to a predetermined physical quantity. Further, a relational expression generation means 1e generates a relational expression indicating the correlation between the number of meshes constituting the polyhedron and the error. In addition, a means 1g for determining the number of error guarantee meshes assigns an allowable error to the relational expression, and calculates the number of error guarantee meshes guaranteeing the allowable error; and the polyhedron generation means 1b generates error guarantee polyhedral data 1h having meshes corresponding in number to the error guarantee meshes.

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