This overtube has a distal-end-side tubular portion that is provided with a first channel through which a manipulator is made to pass and a second channel through which an endoscope is made to pass, and that has flexibility to be driven in accordance with motions of the endoscope and a proximal-end-side tubular portion that extends the first channel toward a proximal-end side from a proximal end of the distal-end-side tubular portion, wherein distal-end openings of the first channel and the second channel are provided at a distal end of the distal-end-side tubular portion, a proximal-end opening of the second channel is provided at the proximal end of the distal-end-side tubular portion, and a proximal-end opening of the first channel is provided at a proximal end of the proximal-end-side tubular portion.
