To rapidly and efficiently design a member of excellent appearance by detecting the collision between adjacent surfaces with each other in bending a model, analyzing the collision, designing a corrected flat sheet metal member of a model to be bent without any collision to eliminate the collision.

A flat sheet metal member of a 2D model designed by a CAD system is bent to a 3D model expressed by the CAD system. A first surface of the sheet metal member expressed by the CAD system is collided with a second surface, and a device to eliminate the collision is provided. The device detects each collision between adjacent surfaces with each other in bending the 2D model to the 3D model by a detecting means. The collision is analyzed by an analyzing means. Collision is eliminated by designing a corrected flat sheet metal member of the 2D model to be bend without generating any collision by an eliminating means.