PURPOSE: To process the division and the integration of a surface in real time and to make possible the division and integration of the surface stretching over a drawing contour, in the surface data having a topology structure.

CONSTITUTION: A surface data integration processing part 3 defines one of the surfaces to be integrated which are instructed from an input/output part 1 as a reference surface, substitutes the arc matching with the arc of other surface of the arcs of a certain reference surface for the arc except the arc matching with other surface and defines the arc as a new arc list. A surface data division processing part 4 determines the intersected point of a surface to be divided and a dividing line, divides the arc of the surface at the intersected point, determines each of the plural arcs composing the left side surface and the right side surface of the dividing line and defines each arc as a new surface. At this time, only one arc on the same surface is left and the updates of the arcs of adjacent surfaces are also performed. As for the surface stretching over a drawing contour, the integration and the division processing may be performed for evey drawing contour.