To provide a ring body with an extended and contracted diameter state maintaining structure, in a connecting structure of a pipe line provided with front and rear two grooves on the inner peripheral surface of a socket 1, installing a ring seal and a partly notched ring body in the deep side groove line and the outlet side groove line, respectively, formed with recessed lines circumferentially in arbitrary positions on the outer peripheral surface of a connecting pipe and engaging the ring body with the recessed line with the connecting pipe inserted in a socket to prevent the pipe line from slipping off.

A locking projection 42 projecting to the outer periphery is formed at a notch of a ring body. An opening 13 in which a locking portion is accommodated in both extended and contracted diameter states is formed in a ring body mounting groove. A hooking step 14 for extending a diameter in which a locking projection is locked with the ring body brought into the extended diameter state is formed at one of the front and rear edges of the opening. A hooking step 15 for contracting a diameter in which a locking projection is locked with the ring body brought into the contracted diameter state is formed at the other edge.