An object is to move a treatment tool (7) in a wider treatment area in real time, while performing treatment. A treatment-tool adaptor (2) of the present invention includes: an adaptor body (15) that is secured to the tip of an insertion portion (8) of an endoscope； a movable member (16) that is disposed along the longitudinal direction of the insertion portion (8) and that supports the tip portion of a treatment-tool channel member (4) through which a treatment tool (7) is passed； and a moving mechanism (17) that causes the movable member (16) to translationally move relative to the adaptor body (15) in a direction intersecting the longitudinal axis of the treatment-tool channel member (4) supported by the movable member (16).
