PURPOSE: To effectively prevent casting defect in term of misrun, blowhole, shrinkage cavity, etc., in casting a precision casting, in particular, thin thickness/ complicated shape product.

CONSTITUTION: An appropriate number of vent holes 26 communicating with a mold cavity 34 are pierced to suitable places of a mold 24. A molten metal is cast in the mold 24, the gas in mold cavity 34 is purged through the communicating hole 26 to outside. By this method, the replacement from the molten metal cast in cavity 34 to gas is promoted and good run of molten metal is achieved.