The advancing / retreating aid for the treatment instrument includes a base having a through hole, an attachment portion for attaching the base to the endoscope so that the through hole faces the treatment instrument insertion port of the endoscope, and an inside through the penetration A first cylinder attached to the base so as to communicate with the hole； and a fixing portion for fixing the treatment instrument inserted into the treatment instrument insertion port, and the first cylinder along the central axis of the first cylinder. A second cylinder that slides in a forward / backward direction with respect to one cylinder, and an advancing / retracting mechanism that moves the second cylinder forward / backward along the central axis by rotating the second cylinder； The second cylinder is urged in a predetermined direction along the central axis with respect to the base with an urging force smaller than the resistance force when the second cylinder slides, and the advance / retreat mechanism is in one direction. And an auxiliary part for assisting the rotation when rotating to the right.処置具の進退補助具は、貫通孔を有するベースと、前記貫通孔を内視鏡の処置具挿入口に対向させるように、前記ベースを前記内視鏡に取り付ける取付部と、内部が前記貫通孔と連通するように前記ベースに取り付けられる第１の筒と、前記処置具挿入口に挿入される処置具を固定する固定部を有するとともに、前記第１の筒の中心軸に沿って前記第１の筒に対し進退方向に摺動する第２の筒と、回転させることにより、前記第２の筒を前記第１の筒に対し前記中心軸に沿って進退移動させる進退機構と、前記第２の筒が前記摺動する際の抵抗力より小さい付勢力で、前記第２の筒を前記ベースに対して前記中心軸に沿った所定の方向に付勢し、前記進退機構が一つの方向に回転する際に前記回転を補助する補助部と、を具備する。
