Silicone (93) is placed between an upper die (65) and an injection-pressing rubber-lid upper die (67), and the silicone injection passage (75) is pressurized by the injection-pressing rubber-lid upper die (67). With this, the silicone (93) is caused to flow into an injection port (77) through the silicone injection passage (75). Then, sequentially through the injection port (77) and the disc silicone-flow passage (73), the silicone is caused to flow toward an inner periphery (71a) of a silicone injection space (71). Further, the silicone flows between both circumferential sides of the silicone-flow deflection region (81). In this way, the silicone flows in a peculiar manner in conformity with a shape of the silicone-flow deflection region (81).