The advancement/retraction assisting tool for a treatment tool according to the present invention is provide with: a base having a through-hole an attachment part for attaching the base to an endoscope so as to cause the through-hole to face a treatment tool insertion port of the endoscope a first cylinder attached to the base so that the inside thereof is communicated with the through-hole a second cylinder for sliding in an advancement/retraction direction with respect to the first cylinder along the center axis of the first cylinder, the second cylinder having a fixing part for fixing a treatment tool inserted in the treatment tool insertion port an advancement/retraction mechanism for rotating the second cylinder and thereby moving the second cylinder in advancing/retracting fashion along the center axis relative to the first cylinder and an assisting part for urging the second cylinder in a predetermined direction along the center axis relative to the base by an urging force smaller than a resistance force occurring during the sliding of the second cylinder, and assisting the rotation when the advancement/retraction mechanism rotates in one direction.Loutil daide à lavancement/rétraction pour un outil de traitement selon la présente invention comprend : une base ayant un trou traversant une partie de fixation pour fixer la base à un endoscope de façon à amener le trou traversant à faire face à un orifice dinsertion doutil de traitement de lendoscope un premier cylindre fixé à la base de sorte que son intérieur communique avec le trou traversant un second cylindre pour coulisser dans une direction davancement/rétraction par rapport au premier cylindre le long de laxe central du premier cylindre, le second cylindre ayant une partie de fixation pour fixer un outil de traitement inséré dans lorifice dinsertion doutil de traitement un mécanisme davancement/rétraction pour faire tourner le second cylindre et ainsi déplacer le second cylindre de manière à avancer/se r
