This overtube has a distal-end-side tubular portion (15) that is provided with a first channel (8) through which a manipulator is made to pass and a second channel (9) 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 (16) that extends the first channel (8) toward a proximal-end side from a proximal end of the distal-end-side tubular portion (15), wherein distal-end openings (20, 21) of the first channel (8) and the second channel (9) are provided at a distal end of the distal-end-side tubular portion (15), a proximal-end opening (22) of the second channel is provided at the proximal end of the distal-end-side tubular portion (15), and a proximal-end opening (23) of the first channel is provided at a proximal end of the proximal-end-side tubular portion (16).
