An endoscope system includes an endoscope and a plurality of over-tubes provided with tube insertion sections having flexibility, through which an insertion section of the endoscope is inserted, and balloons to be expanded and contracted disposed on distal end sides of the tube insertion sections, in which at least outer diameters of the tube insertion sections are different from one another. A size relation of effective lengths of the respective tube insertion sections in the plurality of over-tubes is set to be opposite to a size relation of outer diameters of the tube insertion sections.
