To prevent weld lines, fibrous wrinkles or the like from being produced by providing in a cavity a gas introducing bore in the position different from that of a gate for injecting a resin, so as to inject the resin while applying a gas dynamic pressure from the gas pressure introducing bore.

A coupling rod type of vibration control device is molded by setting to an injection mold an assembly having a rubber elastic material formed by vulcanization and adhesion around an inner cylinder for coupling with the other member, and inserting the assembly. In this case, a cavity 10 has a gate 12 and a gas pressure introducing bore 14 which are disposed to face each other, and a pressurized gas 15 is a nitrogen gas. The position of the gas pressure introducing bore 14 is properly determined according to the cavity shape, kinds of the resin, the gate position or the like.