A cover system endoscope apparatus in which an insert part cover sheath for isolating the insert part of a cover endoscope is airtightly connected to a distal end constructive part of a tip part of an insert part cover. The insert part cover sheath is composed of a soft resin such as polyurethane exhibiting an excellent chemical resistance and a relatively high flexibility. The tip side of the cover sheath is connectively covered on an outer peripheral edge of the rear end of the distal end constructive part. The insert part cover sheath is formed with a forceps inlet on its near-at-hand side. Connected airtightly thereto is an endoscope manipulation part fixing mouth part having an expansion tube mouth for connecting an expansion tube and further a connecting part connected to a cover holding tool. An opening of an endoscope insert channel provided in an interior of the insert part cover sheath is formed on the near-at-hand side of the endoscope manipulation part fixing mouth part. The tip of the endoscope manipulation part fixing mouth part is connected to the distal end constructive part of the cover. Protruded are conduits such as air and water supply conduits and a channel communicating with a forceps outlet. These conduits are each formed of a soft resin such as PTFE exhibiting a low flexibility but a relatively high rigidity. A flexural rigidity when combining these conduits is larger than a flexural rigidity of the insert part cover sheath.