Patent ID: 7914444

Claim:
An endoscope system, comprising: 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 adapted to allow a first treatment instrument to be inserted thereinto; 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 adapted to allow a second treatment instrument to be inserted thereinto, wherein a first distance between the first treatment instrument channel opening and the first observation window is shorter than a second distance between the second treatment instrument channel opening and the second observation window, and the first distance is a tangent of one-half of the first viewing angle, multiplied by a predetermined constant, and the second distance is a tangent of one-half of the second viewing angle, multiplied by the predetermined constant so that the first treatment instrument is allowed to be in a range of the first viewing angle and the second treatment instrument is allowed to be in a range of the second viewing angle when an amount of projection of the first treatment instrument from the first treatment instrument channel opening is longer than a predetermined value and an amount of projection of the second treatment instrument from the second treatment instrument channel opening is longer than the predetermined value.