To provide a connection structure of a triple-layer pipe which eliminates the need for a special tool, which facilitates prompt connection work at a construction site, which facilitates maintenance such as a periodic check, and which can demonstrate a powerful slipping-off avoiding function by making efficient use of characteristics of the triple-layer pipe.

An inner layer 3 and an outer layer 4 made of a synthetic resin are formed on the inner surface side and the outer surface side of an intermediate layer 2 of the triple-layer pipe 1. The intermediate layer 2 is made of a light metal such as aluminum. Then the end 1A of the triple-layer pipe 1 is flare-processed, and is formed in a horn shape. Then a coupling 5 and a cap nut 13 are fastened and connected to each other by male and female screw parts 13c, 8c so that the horn-shaped end 1A is inserted and fixed between a taper-shaped outer peripheral surface part 8b formed on the outer peripheral surface of the cylindrical connected outlet 8 of the coupling 5, and a taper-shaped inner peripheral surface part 13b formed on the inner peripheral surface of the cap nut 13. Thus, the triple-layer pipe 1 engaged with the outer periphery of the cylindrical connected outlet 8 of the coupling 5 is connected and fixed to the coupling 5.