Abstract: A reinforcing bar binding device of simple structure and light weight capable of preventing exposure of wire from concrete which may cause corrosion of reinforcing bar, by reducing the height of the twisted portion of a wire rope, comprising a main body 1, and a loop forming unit 3 having a pair of curved members 2A, 2B with grooves disposed at the leading end of the main body 1 so as to be free to open and close, in which the main body 1 comprises a wire feeder 5 for forming a loop of wire 4 by feeding the wire 4 into the grooves of the pair of curved members 2A, 2B in a closed state so as to enclose the intersection of reinforcing bars 60, and a driving mechanism 6 incorporating a motor 21 for opening or closing the pair of curved members 2A, 2B and, after forming the loop, advancing and retracting a cutter 36 for cutting off the wire 4 being sent out to the grooves, twisting the formed loop, and advancing, retracting and rotating a pair of pin members 37 disposed at an interval for binding the reinforcing