To join an elbow with a service tee more firmly, and surely prevent gas from leaking even when the elbow comes out of its junction point with the service tee.

When an aseismic reinforcing cover 50 is mounted to a joint point between a service tee 20 and an elbow 30, a semi-cylindrical parts 53 of a cover body 51 are hermetically fixed to the service tee 20, and concurrently, the elbow 30 is hermetically and slidably pressed with pressure by semi- cylindrical parts 56 so as to be fitted therein. By this constitution, when the underground is fluctuated to a great extent by earthquakes and the like, and even if the service tee 20 and the elbow 30 are subjected to intensive tension force relatively in the opposite directions so as to be out of their junction point, the elbow 30 will not come out of the aseismic reinforcing cover 50, it is rather closely pressed with pressure so as to be held therein, gas is thereby surely prevented from leaking.