An object of the invention is to provide a mantle tube capable of being firmly held in a desired bending shape, and a treatment tool comprising the same. As shown in Fig. 12 , a mantle tube 3 according to the invention is characterized by comprising a bendable member 10, which is formed in such a way as to be received in an elongate, annular, cylindrical member 9, includes two fixed sites that are fixed to the cylindrical member 9 and a bendable site 13 that is interposed between these fixed sites and bendable in a direction intersecting a longitudinal direction thereof, an angle adjustment member 20 that is capable of adjusting a bending angle of the bendable site 13, and an angle holding mechanism 30 that is capable of holding, at any desired bending angle, the bendable site 13 bent by the angle adjustment member.
