PURPOSE: To enable the firm mounting of an end-cap and to maintain the lightening with cavity parts, by providing notches which open each cavity part to a required length at rear side, by setting up terminal ends of a molding in a mold under recessing a sealing piece protruding from mold surface in the cavity parts through each notches, and by filling a molten resin injected into this mold to the inside of the cavity parts closed by the sealing piece.

CONSTITUTION: Notches C are formed at the rear side m of a molding M. A sealing piece 12 which protrudes in comb-form from the inner surface of a core mold 11 is recessed to each cavity part S of the molding M to the inner side from notched places. Thereby the molding M is positioned towards longitudinal direction and also the inside of the cavity is closed from a place slightly inside of terminal ends. When a molten resin forming an end-cap is injected at this state, the end-cap part E1 is formed in the space of the cavity mold 10. AT the same time the molten resin flows into the cavity parts fitted with sealing piece 12, and an intermeshing part E2 is formed integrally with the end-cap part E1.