A medical tube which is highly flexible and has a very small diameter and a flexibility-variable mechanism having the medical tube are provided. The medical tube includes an interior tube and a plurality of annular segments of a cylindrical shape into which the interior tube is inserted. The medical tube is configured by sequentially connecting the plurality of annular segments while the interior tube is inserted inside of the plurality of annular segments. Each annular segment includes a fitting portion that allows any other annular segment to be fitted to the annular segment, and a fitted portion which may be fitted on the fitting portion of any other annular segment, which has a diameter that increases toward an end of the annular segment and includes at least one slit extending in a direction crossing a diametric direction. When the spacing of the slit is narrowed, the fitting portion of the annular segment and the fitted portion of any other annular segment are engaged with each other so that the annular segments are fixed to each other.
