PURPOSE: To enable control of a shrinkage rate by incorporating ultrafine alumina powder into a phosphate molding material contg. aggregate, thereby constituting the molding material.

CONSTITUTION: The molding material is formed by incorporating the ultrafine alumina powder into the phosphate molding material contg. the aggregate consisting of silica and cristobalite. The content of the ultrafine alumina powder is specified to 1W10pts.wt. per 100pts.wt. molding material. The component having the larger coefft. of expansion of the cristobalite as a refractory material plays the role of the same refractory material and the shrinkage is suppressed by the addition of the alumina having the smaller coefft. of friction, by which the shrinkage rate is controlled.