Provided is an assist tool for advancing and withdrawing a treatment tool, said assist tool making it possible to prevent treatment tool breakage and the like and improve workability for technicians and assistants. The assist tool assists the movement of a treatment tool and is provided with: a flexible tube (55) having formed therein an insertion path (58) for inserting a treatment tool (13) that is inserted in a channel in an insertion section (17) of an endoscope (12) a tube path member (62) that is connected to the flexible tube (55), that comprises a curved part at an intermediate location along the overall length thereof, and in which the insertion path (58) for the treatment tool is formed by a rigid tube body a connecting section (45) connected to the tube path member (62) and formed so that the channel and the insertion path (58) of the tube path member (62) are connected and a holding section (56) that is mounted to the flexible tube (55) and that holds the insertion section (17) of the endoscope (12) or an operating section (16) for the endoscope (12) which is connected with the insertion section (17).Linvention concerne un outil dassistance pour avancer et retirer un outil de traitement, ledit outil dassistance permettant dempêcher une rupture doutil de traitement et analogue et daméliorer la maniabilité pour des techniciens et des assistants. Loutil dassistance assiste le mouvement dun outil de traitement et comprend : un tube flexible (55) ayant, formé en son sein, un trajet dinsertion (58) pour insérer un outil de traitement (13) qui est inséré dans un canal dans une section dinsertion (17) dun endoscope (12) un élément de trajet de tube (62) qui est relié au tube flexible (55), qui comprend une partie incurvée à un emplacement intermédiaire le long de sa longueur totale, et dans lequel le trajet dinsertion (58) pour loutil de traitement est formé par un corps de tube rigide une section de liaison (45) reliée à lélément de trajet de tube (62) et for
