A medical-manipulator rotation mechanism includes: a cylindrical rotator that is fixed to a treatment part at the distal end and that is supported so as to be rotatable about the longitudinal axis; a long power-transmitting member wound around the rotator; and a folding part that bends the power-transmitting member led out in a tangential direction from the rotator and guides the power-transmitting member toward the proximal-end side, wherein the power-transmitting member is led out in tangential directions at different positions between which a wound part of the rotator around which the power-transmitting member is wound exists.