A ground object is arranged so that it overlaps with a cylindrical object. Inside the cylindrical object, foot data of the ground object is arranged. Since the foot data on the side of a fore-end opening is positioned behind a fore-end face object with respect to view point coordinates, hidden surface removal is carried out for an image of the foot data on the side of the fore-end opening viewed from the view point coordinates by a Z value of a transparent drawn image of the fore-end face object.