To provide a connection structure of a double piping protection tube, facilitating tube installation, capable of being repaired after piping, and of preventing a trouble from occurring in working.

A connecting screw portion is formed on an outer peripheral surface or an inner peripheral surface of one side end of a connecting protection tube 1 so as to be screwed and connected with the connecting protection tube 7. A flange portion 3 is formed on the other side end of the connecting protection tube 1, and a protection tube 8 to be connected can be inserted into the pipe. The protection tube 8 to be connected, into which a loop 4 and an O-ring 6 are inserted, is adjusted in the length using the loop 4 and the O-ring 6 having a peripheral surface relative to the outer peripheral end surface of the flange portion 3 and a through hole 5 in slidable contact with the protection tube 8 to be connected, and by inserting from the side end portion forming the flange portion 3. The loop 4 and the outer peripheral end surface of the flange portion 3 are fastened through the O-ring 6, so that the protection tube 8 on one side is held and fastened by a deformation of the O-ring 6 caused by the clamping force.