A three-dimensional stereoscopic diagram creator creates a three-dimensional stereoscopic diagram including a desired bending angle based on graphic information of a product. A major dimension displayer displays a major dimension, tolerance and the like with respect to the three-dimensional stereoscopic diagram. On the other hand, a test piece displayer displays a test piece of the same material proposed for use as the material used for producing the product. The test piece displayer carries out trial bending on the test piece. A bending angle after a bending load is removed is measured by a bending angle measuring device. A spring back amount setter calculates a spring back amount from a difference in bending angle between before and after the load is removed. A stroke calculator calculates a stroke value relative to the desired bending angle considering the obtained spring back amount. Actual bending is performed on a product piece using the calculated stroke value.