Patent ID: 8240715

Claim:
A connection structure of a tubular connection member and a joint member, comprising: a tubular connection member made of a synthetic resin and having a spiral ridge and a flange with a locking protrusion being formed on one end of its outer peripheral surface; a joint member having at one end a spigot portion that is insertable into the tubular connection member and at the other end a pipe-mounting portion that is connectable to a connecting pipe; and a cap nut that is non-removably and rotatably mounted on the joint member, a spiral groove being formed in its inner peripheral surface, the spiral groove corresponding to the spiral ridge of the tubular connection member, and the cap nut being provided with a detent member, the detent member having a movable portion that is integrally coupled at one end to the cap nut and an extending portion that extends in an axial direction from the movable portion beyond an end face of the cap nut, wherein the spigot portion of the joint member is inserted into the tubular connection member and the cap nut is screwed into the tubular connection member so as to bring the extending portion of the detent member to be locked by the locking protrusion of the flange of the tubular connection member, wherein the locking protrusion has an outer peripheral surface whose diameter smoothly and gradually increases in a radical direction of the flange.