Abstract: A collar having a divided structure and surrounding a fitting connection part between a spigot portion and a socket portion in a sealed state is externally mounted over both pipe portions. A first disengagement blocking part that blocks, by contact, a relative disengagement movement beyond a certain level between the socket portion and the collar is provided at a location where the collar and the socket portion side face each other. A second disengagement blocking part provided with a retaining part in which falling-off resistance between the retaining part and an outer peripheral surface of the spigot portion increases according to a disengagement movement of the spigot portion is provided on a pipe support portion side on one end side in a pipe axis direction of the collar.