The overtube includes a first channel (8) through which the manipulator passes and a second channel (9) penetrating the endoscope, and flexibility to be driven according to the operation of the endoscope is set to be And a proximal tubular portion (16) extending from the proximal end of the distal tubular portion (15) so as to extend the first channel (8) to the proximal side , Distal end openings (20, 21) of the first channel (8) and the second channel (9) are provided at the distal end of the distal end side tubular portion (15), and at the base end of the distal end side tubular portion (22) of the channel (9) of the second channel (9) and the proximal end opening (23) of the first channel (8) is provided at the proximal end of the proximal side tubular section (16).このオーバーチューブは、マニピュレータを貫通させる第1のチャネル(8)と、内視鏡を貫通させる第2のチャネル(9)とを備え、内視鏡の動作に応じて駆動させられる可撓性を有する先端側管状部(15)と、該先端側管状部(15)の基端から第1のチャネル(8)を基端側に延長するように延びる基端側管状部(16)とを備え、先端側管状部(15)の先端に第1のチャネル(8)および第2のチャネル(9)の先端開口(20,21)が設けられ、先端側管状部(15)の基端に第2のチャネル(9)の基端開口(22)が設けられ、基端側管状部(16)の基端に第1のチャネル(8)の基端開口(23)が設けられている。
