To provide a coupling to use a double hose to safely transfer fluid of high temperature and high pressure with no trouble and capable of certainly fixing and connecting it.

This coupling is constituted of a connecting pipe 3 forming a female screw 6 on an inner peripheral surface in the neighbourhood of the other end side of a pipe body winding and forming a plural number of projections 4 on an outer peripheral surface in the neighbourhood of one end side and capable of closely inserting and fitting the projections 4 on an inner surface of a jacket hose 2 and a truncated cylindrical projected part 9 which is a pipe body on one end side outer peripheral surface of which a male screw 7 to be screwed in the female screw 6 of an inner peripheral surface of the connecting pipe 3 is screwed and provided, thinner than an inside diameter of the inner peripheral surface outward from a starting end part of the male screw 7 and thick enough to fit an inside hose 10 which are projectively formed. Additionally, it is constituted of a communicating pipe body 8 of a cross-section roughly stepped shape on which a pedestal part 11 larger in diameter than an inside diameter of the connecting pipe 3 is at least connectively formed on a terminal end part of the male screw 7.