PURPOSE: To enable a molding and a conical coil spring to be molded in one piece by forming a molding by infection with a core, a cavity and a groove formed at their specified positions in a molding die.

CONSTITUTION: A core 3 and a cavity 2 formed conically on the facing of the opened halves of a molding die are provided. In addition, an inner conical face with a conical groove 4 is formed on the molding part of a molding die. Further, a clearance is provided in the opened halves of the molding die in such a manner that a film 5 is formed between the pitches of the conical part of a coil spring. Under this structure, the conical core 3 and cavity 2 in the molding part are formed in an identical die opening direction. Thus, it is possible to form an injection molding and a conical coil spring in a single piece instead of assembling these parts together by a conventional injection molding method. In addition, if the number of coil spring parts increases, their effects will become more significant.