PROBLEM TO BE SOLVED: To provide a flexible tube for an endoscope, which solves a problem of a conventional flexible tube that an outer sheath buckles when the flexible tube is bent frequently.SOLUTION: A spiral tube 74 includes a spring structure. The outer sheath 80 is arranged on the spiral tube 74 while the spiral tube 74 is contracted in the axial direction. By doing so, the outer sheath 80 can be expanded in a predetermined amount in the axial direction of the outer sheath 80 by elastic restoration force of the spiral tube 74. By adjusting the contraction amount of the spiral tube 74, the expansion amount of the outer sheath 80 can be set between 5-15% with respect to the natural length. Alternatively, the spiral tube 74 is made of a shape memory alloy that contracts in the axial direction of the spiral tube 74 when heated. By covering the spiral tube 74 with the outer sheath 80 at a temperature of ≥150°C, the spiral tube 74 contracts in the axial direction by shape restoration effect due to the temperature. After that, the temperature is lowered to or below the shape restoration temperature to expand the outer sheath 80 in the axial direction of the outer sheath 80 and in a predetermined amount by expansion force of the spiral tube 74.
