PROBLEM TO BE SOLVED: To provide an endoscope system capable of easily performing alignment between a predetermined position in the circumferential direction about an axis of a slave endoscope to be protruded from a treatment unit channel of a master endoscope and a predetermined position of the circumferential direction about an axis of an end tip part of the master endoscope.SOLUTION: On an inner surface of a tip cap of a treatment unit channel that opens on a root end side of a treatment unit standing base of a master endoscope, a reference indication 42 is formed along the axial direction in the standing direction of the treatment unit standing base. A monitor 5B for displaying an endoscopic image that has been taken at an inserting part of a slave endoscope which is inserted into the treatment unit channel displays a slave endoscope indication 26 which indicates a possible curving direction of a curved part of the slave endoscope and, when the reference indication 42 formed on the end cap appears in the endoscopic image, the slave endoscope is rotated around an axis to match the indications 26, 42, so that the possible curving direction of the slave endoscope is matched with the standing direction of the treatment unit standing base.
