PROBLEM TO BE SOLVED: To provide a treatment tool insertion tool for endoscopes which enables operation for movement of a treatment tool, while maintaining a field of vision once secured, that is, enables operation for movement of the treatment tool, while holding the endoscope by one hand, by operation for movement of the endoscope.SOLUTION: An opening preset part for forming a slit 11 in the axial direction into which a movement operation assisting tool 4 attached to a treatment tool 3 such as forceps and assisting the operation for movement of the treatment tool 3 is inserted, is provided in the peripheral wall of a treatment tool channel 1 of an endoscope through which the treatment tool 3 is inserted and which is formed of a flexible tube.
