A treatment tool is attached and driven in a state in which a constant initial tensile force is collectively imparted to a plurality of tensile-force transmitting members of the treatment tool. A treatment-tool driving device (1) of the present invention is attached, in an attachable/detachable manner, to a treatment tool (3) provided with at least one pair of tensile-force transmitting members (2) and that drives the treatment tool (3) by means of tensile forces imparted to the tensile-force transmitting members (2), wherein the treatment-tool driving device (1) includes: movable members (7) that are individually attached, in an attachable/detachable manner, to one ends of the individual tensile-force transmitting members (2); a driving source that generates a motive power with which the treatment tool (3) is driven; a motive-power transmitting mechanism (9) that switches between coupling and decoupling between the driving source and the movable members (7), and that transmits, in a coupled state, the motive power from the driving source so as to selectively impart tensile forces to the two movable members (7) attached to the paired tensile-force transmitting members (2); and a biasing means (10) that biases the two movable members (7) in directions in which tensile forces are imparted to the tensile-force transmitting members (2) in a state in which coupling by the motive-power transmitting mechanism (9) is released.