Abstract: In a state in which an insert is fitted to an inner portion of a main mold, a hole passing through from an outer portion of the main mold to a cavity of the insert is provided in the main mold to the insert. An extrusion pin bush is inserted into the hole from a side of an opening portion facing the outer portion of the main mold in the hole. A stopper, which is loosely inserted into an outer periphery of a base end side protruding to the outer portion of the main mold from an inner diameter portion of the extrusion pin bush of the extrusion pin, is attached by screw to a thread portion provided in the opening portion facing the outer portion of the main mold. The extrusion pin bush abuts on a locking portion provided on the side of the opening portion facing the outer portion of the main mold in the hole by the stopper.