This treatment tool for an endoscope includes: a sheath in which is formed a lumen that extends in a longitudinal axis direction and has an inner diameter through which a guide wire can be inserted and an operation part which is disposed on a proximal end of the sheath, is formed substantially tubular with an inner diameter that allows the proximal end portion of the sheath to be inserted, and has a port opened so as to communicate from an inner peripheral surface to an outer peripheral surface. The sheath includes: a slit part which is formed on an outer peripheral surface of the sheath along the longitudinal axis direction of the sheath so as to communicate the lumen and an external portion of the sheath, and which is formed so that an opening width in a peripheral direction of the sheath is smaller than the inner diameter of the lumen and an inlet which has a width greater than the opening width of the slit part, communicates with the lumen, and opens to an outer peripheral surface of the proximal end portion of the sheath. The sheath is fixed to the operation part so that when an opening edge portion of the inlet and an inner opening edge portion that forms an outline of an inner peripheral surface side of the port are projected onto the inner peripheral surface of the port from a direction along a straight line that is orthogonal to a central axis of the lumen and a central axis of the sheath, the opening edge portion substantially matches the inner opening edge portion or the opening edge portion is positioned outside the inner opening edge portion.Linvention concerne un outil de traitement pour un endoscope, qui comprend : une gaine dans laquelle est formée une lumière qui sétend dans une direction daxe longitudinal, et a un diamètre interne à travers lequel peut être inséré un fil-guide et une partie de fonctionnement, qui est disposée sur une extrémité proximale de la gaine, a une forme sensiblement tubulaire avec un diamètre interne qui permet à la partie
