There is provided a catheter in which it is possible to improve work performance even in case of including a window portion. The catheter 1 of the present invention is characterized by including: a sheath 2 which is inserted inside a coelom and which is provided with a window portion 26 through which an inspection wave is passed a detection unit 41 which is movable toward the axis direction of the sheath 2 inside the sheath 2 and which detects the inspection wave and a reinforcement tube 4 which can cover the inner surface or the outer surface of the window portion 26 and which is movable toward the axis direction of the sheath 2.
