PURPOSE: To make the superplastic forming possible by setting the laminated plate of the non superplastic metallic plate sandwiched with the superplastic metallic plates between the upper and lower dies and forming under the conditions of the superplastic behavior.

CONSTITUTION: The non superplastic metallic plate 6, i.e., the metallic plate or the metallic foil, etc., without showing a normal superplastic property is inserted between the superplastic metallic plates 5, i.e., the two phase stainless steel, etc., and so the laminated plate 7 is formed. This laminated plate 7 is set between the upper die 1 and the lower die 2, after it is heated to the temperature at which the superplastic metallic plate 5 shows the superplastic property, while on the one side the pressure medium is supplied from the supplying path 3 and the static hydraulic pressure is added, on the other side the air of the inside of the lower die 2 is exhausted from the degasing hole. Therefore, even for the metallic plate which is not possible to be formed with the normal forming method, it is possible to form with the superplastic forming.