PURPOSE: To lift restrictions on enlargement of suction/discharge port area of an electric machine frame and on installation of the discharge port by insertion burying a shutter at a vent in the electric machine frame produced by pouring casting molten metal.

CONSTITUTION: Inserting intermediate die 27' for vent comprises two split dies and a shutter metal 29 component is disposed therein. Outer peripheral main die 31 for providing the outer peripheral side of stator frame is constituted by mating two dies on surface A. A discharge port die 27' for the vent is then secured to an inner peripheral die 32 for providing the inner peripheral profile of the stator frame and it is further secured in the outer peripheral main die 31. Formable beads are then poured into a gap between the outer peripheral main die 31 and the inner peripheral die 32 thus producing a lost foam pattern. After shaping, the lost foam pattern is subjected to coating and filled with sand. Thereafter, casting molten metal is poured and the shutter metal is insertion buried in a cast product.