Abstract: An endoscope capable of adjustably changing the rigidity of the middle portion of the scope section. The endoscope include a middle portion constructed by using a composite helical tube formed by outer and inner helical tubes of different winding radii which are wound coaxially, and a controller for controlling a rigidity of the middle portion by changing a winding radius of the inner helical tube while the outer helical tube is immovably fixed. The outer and inner helical tubes are preferably wound at the same winding pitch in the same winding direction, and arranged such that each winding loop of each one of the outer and inner helical tubes is facing a clearance between adjacent winding loops of another one of the outer and inner helical tube.