PROBLEM TO BE SOLVED: To provide an implement for inserting a treatment instrument for an endoscope, allowing a user to advance/retreat the treatment instrument while retaining a once-secured visual field by the advancing/retreating operation of the endoscope, which means, to advance/retreat the treatment instrument while holding the endoscope by one hand.SOLUTION: A slit 11 is formed in the axial direction on a peripheral wall of a treatment instrument channel 1 of the endoscope, into which the treatment instrument 3 such as forceps is inserted, to insert an advancing/retreating operation aid 5 for assisting the advancing/retreating operation of the treatment instrument 3.
