To provide coupling structure to simplify coupling structure and reduce the size thereof, and besides have high reliability of a seal as a coupling for a piping for high pressure fluid.

The insertion part 22 of a piping 2 on the fuel feed side is inserted in the second fit-in surface 32 of a receiving part 3 integrally formed at a piping 1 on the internal combustion engine side through welding W. A flange 34 on the receiving side formed at the receiving part 3 and a flange 21 on the insertion side formed at a piping 2 on the fuel feed side are brought into contact with each other. Through insertion of the insertion part 22, an O-ring 4 is radially compressed and a proper squeeze margin is brought into close contact with the groove bottom of an O-ring mounting groove 35 and the outer peripheral surface of the insertion part 22. Semiarcuate clamps 5A and 5B are fitted in the two flanges 34 and 21 brought into contact with each other from the outer peripheral side for annular assembly and an annular spring 6 is elastically fitted in the annular spring mounting grooves 52 of the clamps 5A and 5B. This constitution brings the piping 1 on the internal combustion engine and the piping 2 on the fuel feed side into an intercoupling state through the receiving part 3.