PURPOSE: To improve the strength of a formed product by placing a superplastic metalic plate of specified temperature on a member for forming unevenness, and giving superplastic deformation by fluid pressure, and at the same time, coupling it to the member for forming unevenness.

CONSTITUTION: A wire net, expand metal, etc. made of materials or high strength such as steel or stainless steel are used for the member for forming unevenness, and superplastic Al alloy, etc., is selected as the superplastic metallic plate. The member for forming unevenness is placed on a die, and the superplastic Al alloy plate of about 0.5W3mm thick is placed thereon, and heated to superplastic temperatures of about 400W585°C. Then, it is pressed by air pressure of about 10kg/cm2, and the Al alloy plate is superplastically deformed and coupled to the member for forming unevenness. As a thin superplastic metallic plate and a member of high strength are coupled by this method, the strength of the product is improved.