An advance and retreat assist tool (100) includes a base unit (300), a fixing unit (400) which fixes the base unit (300) to an endoscope (10) and a first tubular member (500) into which a treatment instrument (51) is inserted and which guide the treatment instrument (51) to the endoscope (10). The advance and retreat assist tool (100) further includes a fixing portion (600) which fixes the treatment instrument (51) to the first tubular member (500), a rotary portion (700) which provided in the first tubular member (500) and an advance and retreat mechanism (800) which advances and retreats the first tubular member (500) on the basis of the a rotation force of the rotary portion (700).
