To provide a method not requiring an additional process, not using a harmful catalytic substance and eliminating the formation of formaldehyde while achieving a faster thermal de-binding speed as compared with a known method by using a standard apparatus.

In a process forming a binder compsn. by mixing a first binder and a second binder, the first binder has at least vapor pressure of 1Torr (133.3Pa) at the decomposition temp. of the second binder and the binder compsn. is mixed with one or more kind of a granular substance at temp. equal to or higher than the m.p. of the binder compsn. to form a supply raw material. Next, a part is formed from the supply raw material by injection molding and heated at a speed of 0.5-10°C/min.