An advance and retreat assist tool includes a base unit, an attachment portion which attaches the base unit to a treatment instrument insertion portion, a tubular member provided to advance and retreat relative to the base unit coaxially with a central axis of a hole portion and a fixing portion which fixes an endoscopic treatment instrument to the tubular member. The advance and retreat assist tool further includes a rotary portion which has an axis different from an axis of the tubular member and which rotates around the axis, and an advance and retreat mechanism.
