An endoscope system includes a first endoscope that includes a first distal end portion, a first observation window provided at the first distal end portion, a first objective optical system optically coupled to the first observation window and having a first viewing angle, and a first treatment instrument channel opening positioned at a first distance away from the first observation window; and a second endoscope that includes a second distal end portion, a second observation window provided at the second distal end portion, a second objective optical system optically coupled to the second observation window and having a second viewing angle wider than the first viewing angle, and a second treatment instrument channel opening positioned at a second distance longer than the first distance.