PURPOSE: To reduce the manufacturing stages, to simplify an equipment and to prevent the generation of defects such as cracking and dimensional shrinkage in the preform by manufacturing the preform by a dry method in the use of organic fibers as a shape-retaining agent.

CONSTITUTION: For example, organic fibers 2 such as cellulose fibers and the powder of sodium silicate 3 as an inorganic binder, about 0.1 to 10wt.%, are added to ceramic whiskers 1, which is housed in a vessel 4 and is sufficiently stirred and mixed. Next, the mixture 5 is housed in a die 6 and is formed by a piston 7 under about 10 to 500kgf/cm2 pressurizing force to obtain a preform. The organic fibers forming the preform do not become impurities because they disappear at the time of preheating the preform to the same degree to a molten metal in the stage of compounding the preform with the molten metal.