An air/water channel is split into smaller-diameter branch channels before the air/water channel enters a bending portion so as to create a space within a joint ring constituting the bending portion. A forceps channel having the largest outer diameter among internal components of the joint rings is disposed at the center of the joint rings. In addition to the branch channels, optical fibers as a light guide, a signal line, and the like are arranged around the forceps channel within the joint rings. By eliminating the created space, a diameter of the joint rings is reduced and thus a diameter of an insertion section is reduced.
