A placement position of a sketched image into a three-dimensional space and viewing point direction are determined using the angle method or the three-point method, and the cross-section lines of a door cross-section line and center cross-section line of a vehicle depicted in the sketched image is determined and, based on the obtained cross-section line and center cross-section line, a spatial curved surface of the vehicle in the three-dimensional space is determined, distortion is corrected, and a curved surface is created.