PURPOSE: To enable a product of complicated form with reverse taper to be molded in a single molding process by a single seamless molding die by mixing a shape retaining agent varying reversibly form softening to hardening or from low viscosity to high viscosity into molding die materials, and forming a molding die cavity in the area of hardening or high viscosity temperature area of the shape retaining agent.

CONSTITUTION: A shape retaining agent varying reversibly from softening to hardening and from low viscosity to high viscosity is used. The typical ones are rubber, Metolose and hydroxyethyl cellulose. The shape retaining agent is mixed with powder of ceramics, metal, resin or the like in which a master model is filled. Filling is carried out in the area of low viscosity or softening temperature area of the shape retaining agent, and when the temperature is varied for high hardness or high viscosity, a die is extraordinarily strengthened following hardening or turning into high viscosity of the shape retaining agent. At said stage, the master model is removed by transforming, melting or vaporizing to form a cavity. When, for instance, slurry, for casting of a ceramic wave, containing approximately 30 % water content is poured into the die, water in the slurry is absorbed by the die, and wall-forming is effected. As being cooled, the shape retaining agent is reformed into the original agueous solution, and the die is recovered to the state of flowability, the molded production inside may be removed out of the die without any damages.