A treatment-tool adaptor including: an adaptor body that is secured to the tip of an insertion portion of an endoscope a movable member that is disposed along the longitudinal direction of the insertion portion and that supports the tip portion of a treatment-tool channel member through which a treatment tool is passed and a moving mechanism that causes the movable member to translationally move relative to the adaptor body in a direction intersecting the longitudinal axis of the treatment-tool channel member supported by the movable member.
