Provided is a bendable treatment instrument which enables a leading end section thereof having a device attached thereto to be freely bended independently of a flexible endoscope, and can prevent the device from being twisted due to a twist, about the axis, of a sheath wire member caused when insertion into the flexible endoscope is performed, and which has no possibility of causing any impediment to arrangement or movement of a person or an object when the flexible endoscope is pivoted. The bendable treatment instrument is provided with: a bendable part 4 which has a treatment member attached to the leading end thereof a manipulation part which allows bending operation of the bendable part 4, opening and closing operations of forceps serving as the treatment member, and advancing and retracting operations of a surgical knife serving as the treatment member a sheath wire part 5 through which manipulation performed with the manipulation part is transmitted and an axial fixation means 100 which prevents the sheath wire part 5 from rotating about the axis thereof. The axial fixation means 100 is provided with: an engagement protrusion 105 fixed to the sheath wire part 5 and an axial fixation part 104 in which a groove 104a is formed so as to be engaged with the engagement protrusion 105, and which allows the sheath wire part 5 to move in the axial direction but prevents the sheath wire part 5 from rotating about the axis thereof. An end section, on the bendable part 4 side, of the axial fixation means 100 is curved such that the axial fixation means 100 and the pivoting center axis of a flexible endoscope become parallel to each other when the axial fixation means 100 is held by an endoscope channel.Linvention concerne un instrument de traitement pliable qui permet à une section dextrémité avant de ce dernier ayant un dispositif solidaire associé dêtre librement plié indépendamment dun endoscope flexible, et qui peut empêcher le dispositif dêtre torsadé en raison dune
