A surgery system includes an overtube that has a distal end, a proximal end, and a longitudinal axis and holds a treatment tool and an endoscope so as to be movable forward and backward in a direction of the longitudinal axis. The overtube has an endoscope holding part that has an endoscope holding surface for holding the endoscope and allowing circumferential rotation of the endoscope about a central axis of the endoscope, and a treatment tool holding part that has a treatment tool holding surface for holding the treatment tool. The surgery system further includes an endoscope that is inserted into the overtube and has a held surface held by the endoscope holding surface. The endoscope has an orientation maintaining part that maintains the circumferential orientation of the endoscope even in a case where the overtube rotates around the longitudinal axis.