To provide a joint structure of double piping which is able to reduce production cost by facilitating manufacturing and assembly work through curtailment of the number of parts for supporting internal pipes, to prevent breakage of internal pipes, and to enhance durability of these pipes.

A flange 25 is attached to the external circumference of the terminal portion of an external pipe 20 which constitutes double exhaust piping 14, while a flange 26 is adhered to the external circumference of the terminal portion of a suction pipe 24 which is connected to the external pipe 20. A ball-joint gasket 27 is inserted into a gap between 25b and 26b which are seal seats of the flange 25 and flange 26, respectively. On its internal circumference face, an inner pipe holding unit 27c is formed in a unified body with the internal circumference surface of the internal pipe holding unit 27c arranged to face the external circumference of the inner pipe 21 which constitutes the double exhaust piping 14 through an intermediate of a gap G. A bolt 28 is arranged to pierce through insertion holes 25a and 26a of the flange 25 and 26 while a coil spring 29 is put between the head 28a of the bolt 28 and the flange 26, and a nut 30 is screwed into the tip portion of the bolt 28.