The medical treatment endoscope according to the present invention includes a sheath having a flexibility; at least one arm member having a bending part that projects out from a front end of the sheath and performs bending actions; an open/close mechanism which directs the arm member from a direction along a central axis of the sheath to a direction deviated from the central axis of the sheath, and from a direction deviated from the central axis of the sheath to a direction along the central axis of the sheath; and a viewing device and an illuminating member that are disposed to the front end side of the sheath. In the medical treatment endoscope, the front end of the arm member is capable of relative displacement with respect to the viewing device and the illuminating member by means of at least one of a bending action of the bending part and a directional transition of the arm member by the open/close mechanism.