[Problem] To provide an outer sleeve tube that can be held in a fixed manner in a desired curved-shape, and a treatment tool having the outer sleeve tube. [Solution] This outer sleeve tube (3) is characterized by being provided with the following: a curving member (10) having curving segments (13) that are formed so as to be able to be accommodated in an annular and narrow cylindrical member (9) and that are disposed at two fixed segments fixed in the cylindrical member (9) and disposed between the fixed segments, and that can be curved in a direction that intersects the longitudinal direction of the curving portions, and the curving member causing the cylindrical member (9) to be curved in accordance with the curving segments (13) in a direction intersecting the longitudinal direction an angle adjusting member (20) that can adjust the curvature angle of the curving segments (13) and an angle maintaining mechanism (30) that can maintain at any angle of curvature the curving segments (13) that have been curved by the angle adjusting member (20).La présente invention vise à proposer un tube de manchon externe, qui peut être maintenu de façon fixe dans une forme incurvée souhaitée, et un outil de traitement ayant le tube de manchon externe. A cet effet, linvention concerne un tube de manchon externe (3) qui est caractérisé en ce quil comprend : un élément de courbure (10) ayant des segments de courbure (13) qui sont formés de façon à pouvoir être reçus dans un élément cylindrique annulaire et étroit (9), et qui sont disposés sur deux segments fixes fixés dans lélément cylindrique (9) et disposés entre les segments fixes, et qui peuvent être incurvés dans une direction qui coupe la direction longitudinale des parties de courbure, et lélément de courbure amenant lélément cylindrique (9) à sincurver en fonction des segments de courbure (13) dans une direction coupant la direction longitudinale un élément dajustement dangle (20) qui peut ajuster langle de courbure des segm
