To provide a triple-structure pipe of carrying an extremely low temperature fluid such as liquid hydrogen, offering quick separating and joining operation and ensuring explosion-proofing of hydrogen or others.

This triple-structure detachable pipe joint comprises inner pipes 11, 13 for carrying liquid hydrogen A, vacuum isolating pipes 15, 17 encircling these for defining an annular vacuum layer B and outer pipes 23, 25 encircling the vacuum isolating pipes 15, 17 for defining an inactive gas layer C. The ends of the inner pipe 11, the vacuum isolating pipe 15 and the outer pipe 23 as well as the ends of the inner pipe 13, the vacuum isolating pipe 17 and the outer pipe 25 are sealed with annular end plates 27, 29. A quickly detachable joint 40 is provided between the ends of the outer pipes 23, 25 and a port 55 is made in one annular end plate 29 of the annular end plates between which multiple packings are held. The port 55 is communicated with the inactive gas layer C.