An overtube comprises a flexible tubular portion in which an insertion channel is formed. An endoscope is inserted through the insertion channel. A plurality of balloons are loaded at plural positions on an outer surface of the flexible tubular portion. Specially, the balloons are expanded and shrunk selectively every use pattern, and the positions are different from each other in an axial direction of the flexible tubular portion and set to be fixed to an inner wall of either a body cavity or a tubular cavity of an object being examined at mutually different positions of the inner wall by expanding the balloons.
