To provide a formed article without blowing the highly compressed gas in performing the blow forming of a super-plastic sheet, and to prevent the film of residue from being precipitated on the surface of the formed article by using the gas generating agent of metal carbonate in the forming method to transfer the shape of die to the sheet with the gas pressure.

A super-plastic Al alloy sheet 1 of about 1mm in thickness is set to simple dies 2, 3 made of duralmin, the gas generating agent of zinc carbonate of about 0.4g is charged in a circular hole of the lower die 3, and the alloy sheet 1 is fixed by tightening the sheet in the vertical direction by bolts. The simple dies 2, 3 are placed in a heating furnace which is pre-heated at about 260°C, and kept at the temperature for about one hour to perform the forming, and a formed body whose top part is of spherical dome shape is obtained. The formed body can be obtained in this method without blowing the highly compressed gas in performing the blow forming of the super-plastic sheet, and the blow forming method of the super-plastic sheet can be obtained in which no film of the residue is precipitated on the surface of the formed article.