A front end of a ball screw shaft driven by a motor is connected with a binding line clamp apparatus (513) including three clamp plates (514, 515, 516). The left and right clamp plates (515, 516) are constituted to be brought into elastic contact with the center clamp plate (515) and close the left and right clamp plates by operation of cams (527, 528) when a sleeve is moved rearward. In a state of opening the clamp plates, a binding line is fed out to an upper side by passing through an interval between the right clamp plate (515) and the center clamp plate (514), formed in a loop shape and moved into an interval between the left clamp plate (516) and the center clamp plate (517). When the sleeve is moved rearward by driving to rotate a ball screw shaft, the left and right clamp plates are closed to grasp a front end and a rear end of the binding line loop and thereafter, the binding line clamp apparatus is rotated to twist the binding line to bind a reinforcing bar.