Flexible tube and insertion device

A flexible tube for use in an insertion device, comprising:

• a spiral tube having elasticity and including (i) a first area portion which includes an area under an initial tension at a portion along a central axis of the spiral tube, and (ii) a second area portion which is continuous with a proximal end side of the first area portion and which is not under the initial tension;
• and
• a built-in component including at least one coil which is incorporated in the spiral tube and supplements the elasticity of the spiral tube, the built-in component including (i) a first supplement area portion under an initial tension, and (ii) a second supplement area portion which is under an initial tension smaller than the initial tension of the first supplement area portion and which is located on a more proximal end side than the first supplement area portion,
• wherein the first supplement area portion is arranged in the first area portion side, and the second supplement area portion is arranged in the second area portion side, and
• a boundary portion between the first supplement area portion and the second supplement area portion is positioned at a position which is shifted, in a direction of the central axis of the spiral tube, from a position where the first area portion and the second area portion are continuous with each other.