A dividing wall member is provided inside a specific bending piece selected from a plurality of bending pieces, an internal space of the bending piece is divided by the dividing wall member into a first space that opens corresponding to one rotating shaft, of rotating shafts that form a left and right pair, and a second space that is larger than the first space and opens corresponding to another rotating shaft, of the rotating shafts that form a left and right pair, and rotating shafts that form an upper and lower pair, a signal cable is inserted as a first internal component inside a first space, and a pair of light guides and a treatment instrument insertion channel are inserted as second internal components inside the second space.