Abstract: An injection molding die is provided with a cavity block including a stationary mold having first and second split molding cavity portions having different shapes, and a movable mold having first and second common split molding cavity portions, so as to form first and second molding cavities between the stationary and movable molds in mold clamping. Each time a molding shot is performed, a component part to be sealed is inserted while a primary molded piece formed in the first molding cavity is transferred to the second molding cavity and a secondary molded piece formed in the second molding cavity is removed. Thus, the first and second molded pieces can be simultaneously produced.