PURPOSE: To efficiently manufacture a reliable diaphragm by solidly molding a cone part to constitute a diaphragm and an edge part with an injection molding of which material is a thermoplastic synthetic resin.
CONSTITUTION: An edge 17 (same code as a cavity 17) is molded by injecting the melted thermoplastic synthetic resin into the cavity 17 through gates 10, 10a and 10b. The resin being injected into a die flows into the exposure part of a cone 15 in a cavity 16, melt-sticks to the end part of the cone 15 and the cone part and the edge part are made solid. Next, the die is opened by raising a movable die 11 and the diaphragm, of which cone 15 and edge 17 are made solid, is obtained by removing a molded body from a die Y. Thus, the diaphragm showing an excellent sound effect can be easily obtained.