Silicone is placed between an upper die and an injection-pressing rubber-lid upper die, and the silicone injection passage is pressurized by the injection-pressing rubber-lid upper die. With this, the silicone is caused to flow into an injection port through the silicone injection passage. Then, sequentially through the injection port and the disc silicone-flow passage, the silicone is caused to flow toward an inner periphery of a silicone injection space. Further, the silicone flows between both circumferential sides of the silicone-flow deflection region. In this way, the silicone flows in a peculiar manner in conformity with a shape of the silicone-flow deflection region.