The subject innovation is not to combine the exit state, with a double wall pipe must be of a watertight connector provided with a coupling to seal having a withdrawal prevention structure according as to connect the double-walled tube on the double-walled packing tolerance. That is, the present design is formed in a ringsang able to be bonded to the outer periphery of the double wall pipe (110) form a groove 111 a groove engaging portion (10) protruding to be inserted into the binding to the double wall pipe (110) to the inside , to the outside is in close contact with the connection pipe 120 to maintain the water-tight state the outer surface forms a water-tight contact portions 20, the projecting surface and the rear inner surface are be supported by a projecting portion 112 of the double wall pipe (110) It is one with respect to the separating force to form a separation preventing section 30 for generating a separation resistance. Thus, the subject innovation is fitted into the groove of the double wall pipe, with maintaining a water-tight standing because it puts a separation resistance against the separation force, it is possible to quickly and easily to complete the coupling of the double wall pipe, the separation of the separating force due to an external force resistance to generate the will to maintain a solid bond status.