The disclosed technology is directed to a treatment instrument comprises an end effector having a pair of clamping members configured to pivot with respect to one another. A sheath is attached to the end effector along a longitudinal axis so that the end effector can be bent or curved. A drive shaft is connected to the end effector so as to guide the end effector to open or close the pair of clamping members relative to one another when moved in a longitudinal direction relative to the sheath. An elongated member is connected to the end effector and is configured to make the end effector bend or curve with respect to the sheath when moved in the longitudinal direction relative to the sheath. First and second members are configured to produce first and second forces sufficient to open or close the pair of clamping members.
