PURPOSE: To decrease working allowances for cutting after casting by forming the inside diameter of a recessed part formed by casting to the same diameter as far as possible over the entire length.

CONSTITUTION: An auxiliary metal mold 3 in the metal mold structure having the auxiliary metal mold for forming the recessed part in the casting by projecting into a cavity space 10 is formed of a material having the coefft. of thermal expansion equal to or higher than the coefft. of thermal expansion of the molten metal to be poured into the cavity space. The auxiliary metal mold 3 expands to press the molten metal at the time of casting and shrinks larger than the casting at the time of cooling, thereby producing a clearance with the recessed part. There is, therefore, no need for forming a draft taper on the auxiliary metal mold 3 and the need for cutting the recessed part after casting is obviated.