PROBLEM TO BE SOLVED: To provide a medical tube and a flexibility variable mechanism which can provide a flexibility variable medical tube higher in flexibility and smaller in diameter.SOLUTION: A medical tube includes built-in tubes 200 and a plurality of cylindrical node rings 1 interpolating the built-in tubes 200. The plurality of node rings 1 insert the built-in tubes 200 while being successively joined. The node rings 1 are provided with engaging parts 11 which can engage other node rings 1 inside the node rings 1 and engaged parts 12 engageable with the engaging parts 11 of the other node rings 1. The engaging parts 11 are larger in diameter the closer they are toward end parts of the node rings 1, and are provided with at least one notch part 13 extending in the direction crossing a radial direction, and by a gap of the notch 13 of the engaging part 11 of the node ring 1 becoming smaller, the engaging part 11 of the node ring 1 and the engaged part 12 of another node ring 1 are engaged, and the node ring 1 and the other node ring 1 are fixed.
