PROBLEM TO BE SOLVED: To provide an endoscope system that makes it possible to smoothly perform observation and treatment without causing interference between an endoscope and a treatment instrument in a limited working space.SOLUTION: An endoscope system 1 comprises: an endoscope 2 including a rigid insertion unit 21 including at least one first imaging device 11 built-in, the first imaging device having a visual field direction crossing the longitudinal axis 21a direction of the insertion unit； a treatment probe 4 including a slender and rigid probe main body 41； and a mounting instrument 7 including a first through hole 71h1 that functions as a movable mounting unit for the insertion unit 21 of the endoscope 2, and a second through hole 71h2 that functions as a probe fixation unit for arranging the probe main body 41 of the treatment probe 4 along the side of the insertion unit 21.SELECTED DRAWING: Figure 3
