PURPOSE: To prevent a damage of an electroformed hull caused by a heat history of an electroformed mold to remarkably enhance the life of the electroformed mold.

CONSTITUTION: Temperature regulating pipes 2 are disposed behind an electroformed hull 1 of a nickel or the like forming a molding face. A primary backup material 3 is charged. A secondary backup material 4 is further charged behind the material 3. In this electroformed mold, the primary backup material 3 is made of a material, such as a bismuth, having a high thermal conductivity and a linear expansion coefficient identical to that of the material of the electroformed hull. If the electroformed mold is repeatedly expanded and shrunk under heat history at the time of molding, the electroformed hull 1 and the primary backup material 3 are expanded and shrunk in synchronism with other, thereby being prevented from being peeled at the bonding surface thereof.