PURPOSE: To provide a simple execution, to raise a strength of a spiral tube, to recycle the tube even if its diameter is small, and to eliminate buckling damage even if its diameter is large, merely by applying a pressure to water, etc., filled in the tube.

CONSTITUTION: A method for recycling an existing tube comprises the steps of passing a spiral tube 1 through the existing tube 3 while spirally winding a bandlike element having engaging parts at both side edges to form the tube 1, fixing both ends of the tube 1 to the tube 3, sealing both ends of gaps between the tubes 3 and 1 to seal both ends of the tube 1, then fully filling water, etc., in the tube 1, and gradually applying a pressure to the filled water, etc., of the tube 1 while pouring backing material 2 in the gap between the tubes 3 and 1, thereby recycling the tube 3.