To prevent the development of metal penetration and shrinkage cavity.

An aluminum foil 15 is stuck on recessed parts 10, 11 of an upper die 2 and a lower die 11 and also on sand core surface positions 12, 13 faced to the recessed parts 10, 11 with adhesives. At the time of pouring molten aluminum 16 into a cavity 7 in a mold 5, the molten aluminum 16 filled up into the cavity thick parts 8a, 8b is uniformly and rapidly cooled and solidified with the aluminum foil 15 stuck to the recessed parts 10, 11 and the sand core surface positions 12, 13 and the shrinkage cavity is not developed.