An initial polygon obtained from a point group is used as a control polygon, and a control point of the control polygon is offset in a normal direction by the shortest distance from a limit surface generated by the control polygon, so that the position of new control point is determined to allow a subdivision surface to interpolate the initial polygon, thereby generating the subdivision surface which interpolates the point group. A first process to determine the point on the subdivision surface at the shortest distance from each control point, and a second process to move and offset the control point in the normal direction from the surface by the distance between the point on the surface and the initial control point, are iterated until the distance between the initial point group and the point on the surface satisfies the threshold or becomes smaller than the threshold, thereby generating the subdivision surface interpolating the initial polygon. Consequently, the subdivision surface interpolating the point group is generated within a short operation time period, without solving a linear system.