An overtube includes: an endoscope insertion portion passing hole through which an insertion portion of an endoscope is passed and at least one manipulator passing hole through which a manipulator insertion portion of a manipulator apparatus is passed. The manipulator insertion portion includes a driving portion which has at least one first joint and one second joint rotating clockwise and counterclockwise. The endoscope insertion portion passing hole includes an endoscope protrusion amount determination portion which determines a length of a protrusion of the endoscope and an observation optical system observation direction determination portion which determines an observation direction of the endoscope. The manipulator passing hole includes a manipulator protrusion amount determination portion which determines positions of the first joint of the manipulator within the observation optical system and a joint driving direction determination portion which determines rotating directions of shafts of joints within the observation direction.
