A treatment tool includes a sheath that has a distal end portion and a proximal end portion, is formed with a lumen through which a guide wire is insertable, and has an opening portion that is opened in a direction intersecting with a central axis of the lumen on an outer circumferential surface of the proximal end portion while communicating with the lumen; a proximal end holding portion that holds a proximal end region at a proximal end side of the proximal end portion; and a distal end holding portion that holds a distal end region disposed more distal than the proximal end region of the proximal end portion, wherein the distal end holding portion holds the distal end region in a bent state with respect to the proximal end region such that the opening portion is located on an extension of the central axis of the lumen.