An endoscope system 1 includes an endoscope 2 and a plurality of over-tubes 3A, 3B, and 3C provided with balloons 35A, 35B, and 35C to be expanded and contracted on distal end sides of tube insertion sections 31 A, 31 B, and 31 C having flexibility, in which outer diameters of the tube insertion sections 31A, 31B, and 31C are different from one another. A size relation of expansion time diameters Ar, Br, and Cr and a size relation of axial direction lengths Al, Bl, and Cl of the balloons 35A, 35B, and 35C provided in the tube insertion sections 31A, 31B, and 31C of the plurality of over-tubes 3A, 3B, and 3C coincide with a size relation of outer diameters Ao, Bo, and Co of the tube insertion sections 31 A, 31B, and 31C.
