To provide a hinge member of a bending treatment instrument inserted into an endoscope channel and used bendably through intuition and capable of withstanding loads resulting from grasping and resection motions of treatment instruments as well as to provide a bending treatment instrument which uses the hinge member.A hinge member substantially tubular in shape, where a plurality of the hinge members make up a bending treatment instrument by being arranged in a row substantially coaxially with one another, the hinge member including: a pair of recesses formed at least on outer edges of an end face on a proximal side in an axial direction and a pair of projections formed at least on an outer edge of an end face on a distal side by being shifted 90 degrees in a circumferential direction from the recess and facing each other in radial direction, wherein a bending-wire passage hole penetrating the hinge member in the axial direction is formed at a position avoiding the projections on the end face on the distal side, and a device-wire passage hole penetrating an axial center portion.
