Disclosed is a completely nonmetallic pipe connection mechanism for a seal device. In the pipe connecting mechanism of the present invention, a metallic reinforcing pipe (60) is screwed in a through-bore (53) of a flange (50), and a resin connecting pipe (70) is inserted into a through-bore (67) and an expanding diameter portion (68) of the metallic reinforcing pipe (60). Also, a metallic cap (80) is installed in a head (63) of the metallic reinforcing pipe (60), and a large diameter portion (74) of the resin connecting pipe (70) is sandwiched between the metallic reinforcing pipe (60) and the metallic cap (80). Also, a tapered male screw (96) of a resin connector (90) is screwed in a tapered female screw (76) of the large diameter portion (74) of the resin connecting pipe (70) to connect a tube (98) with the resin connecting pipe (70). The tip portion of the resin connecting pipe (70) is provided with an O-ring (72), which is arranged on an expanding diameter portion (16) of the stationary ring (10) to seal between an outer circumference surface of the resin connecting pipe (70) and an inner circumference surface of the expanding diameter portion (16).