PURPOSE: To enlarge the selecting range of a core material and to efficiently form a formed product having various shapes without restriction of the shape by specifying the special core for forming.

CONSTITUTION: The special core 1 for forming is composed of a core body H formed of a material having collapsibility of gravel, etc., of river, sea and mountain and an outer body G made of heat resistant material covering the surface of the core body at a specific thickness. A forming mold 4 is formed by arranging the core for forming between an upper mold 2 and a lower mold 3, and in the forming mold, a cavity part having the shape corresponding to the shape of the formed product 6 is formed. By this method, the improvement of the productivity and the enlargement of the available range are realized and also, the formed product having excellent quality can be obtd. and the forming cost can be reduced.