An endoscope system including an endoscope having an insertion section which extends from a proximal end to a distal end and is inserted into a cavity under inspection and an operation section connected to the proximal end of the insertion section, and a protection cover including an insertion section inserting channel which extends from a proximal end to a distal end and into which said insertion section of the endoscope is insertable and a conduit channel which extends from the proximal end to the distal end, the improvement being characterized in that a distal end portion of the insertion section has a non-circular cross section such as a semicircular or oval cross section and a proximal end portion of the insertion section has a substantially circular cross section. A distal end member of the insertion section inserting channel has an accommodating portion which is a corresponding non-circular cross section.