PURPOSE: To obtain castings having good precision by using a paper core, there by preventing the rapid temp. fall of the castings and preventing the strains generated at the time of the temp. fall by the heat retaining effect of this paper one during the forging.

CONSTITUTION: The paper core 10 formed by injection molding of a mixture composed of paper pellets and plastic pellets is arranged in the cavity of metal molds for forging and molten metal is poured into the cavity. In such a case, the molten metal is mainly cooled by the metal molds for forging, by which the die casting 12 is produced. The paper core does not burn except that its surface scorches. Next, the die casting 12 is put into a container 24 filled with hot water 23 where the die casting 12 is immersed in hot water 23 in a prescribed time. The fibers of the paper part of the paper core 10 are thereby gradually loosened. Next, the paper core 10 is pulled out of the die casting 12 and is discharged outward. The die casting 12 having the good precision is obtd. in such a manner.