A reverse rotational number of a binding wire feed mechanism is set such that a binding wire is completely pulled back regardless of a boldness or flexibility of the binding wire, a diameter of a reinforcing bar or the like. A driven gear 14 having a V groove of the binding wire feed mechanism is brought into elastic contact with a main drive gear 13 having a V groove by a spring and the binding wire is fed by pinching the binding wire by the main drive gear 13 having the V groove and the driven gear 14 having the V groove. After feeding out the binding wire to form a loop around the reinforcing bar and clamping a front end of the binding wire by a twist mechanism, the binding wire feed mechanism is rotated reversely and the binding wire is pulled back to be wound around the reinforcing bar. After stopping the binding wire, the main drive gear 13 having the V groove and the driven gear 14 having the V groove are slipped relative to the binding wire to rotate idly and continue to rotate reversely until a predetermined rotational number.