A binding machine for reinforcing bars (a) comprising: a binding machine body; a bending guide arm arranged at an end of said binding machine body; a feed adjustment mechanism; and a twisting mechanism, wherein a binding wire (b) is sent outside reinforcing bars (a) from said bending guide arm and is formed into a loop, and then a portion of the loop is twisted by said twisting mechanism so as to bind the reinforcing bars (a), wherein said feed adjustment mechanism adjusts a feed of the binding wire (b) according to one of a diameter of the reinforcing bars (a) and a diameter of the loop of the binding wire (b) wound round the reinforcing bars (a), and said feed adjustment mechanism comprises: a motor; a first feed gear rotated by said motor; a second feed gear engageable with said first feed gear; a link connected to said second feed gear; an electromagnet; wherein said second feed gear is engaged with said first feed gear in order to feed the binding wire (b) when said electromagnet is not electrified, wherein said second feed gear is attracted by said electromagnet via said link and disengaged with said first feed gear in order to stop feeding the binding wire (b) when said electromagnet is electrified, characterized in that said feed adjustment mechanism further comprises: a rotary shaft of said first feed gear; a plurality of magnets attached to the periphery of said rotary shaft; a magnetic sensor, wherein the rotating speed of said first and second feed gears (108, 109) is detected by said magnets and the magnetic sensor. a binding machine body; a bending guide arm arranged at an end of said binding machine body; a feed adjustment mechanism; and a twisting mechanism, wherein a binding wire (b) is sent outside reinforcing bars (a) from said bending guide arm and is formed into a loop, and then a portion of the loop is twisted by said twisting mechanism so as to bind the reinforcing bars (a), wherein said feed adjustment mechanism adjusts a feed of the binding wire (b) according to one of a diameter of the reinforcing bars (a) and a diameter of the loop of the binding wire (b) wound round the reinforcing bars (a), and said feed adjustment mechanism comprises: a motor; a first feed gear rotated by said motor; a second feed gear engageable with said first feed gear; a link connected to said second feed gear; an electromagnet; wherein said second feed gear is engaged with said first feed gear in order to feed the binding wire (b) when said electromagnet is not electrified, wherein said second feed gear is attracted by said electromagnet via said link and disengaged with said first feed gear in order to stop feeding the binding wire (b) when said electromagnet is electrified, characterized in that said feed adjustment mechanism further comprises: a rotary shaft of said first feed gear; a plurality of magnets attached to the periphery of said rotary shaft; a magnetic sensor, wherein the rotating speed of said first and second feed gears (108, 109) is detected by said magnets and the magnetic sensor. a motor; a first feed gear rotated by said motor; a second feed gear engageable with said first feed gear; a link connected to said second feed gear; an electromagnet; wherein said second feed gear is engaged with said first feed gear in order to feed the binding wire (b) when said electromagnet is not electrified, wherein said second feed gear is attracted by said electromagnet via said link and disengaged with said first feed gear in order to stop feeding the binding wire (b) when said electromagnet is electrified, characterized in that said feed adjustment mechanism further comprises: a rotary shaft of said first feed gear; a plurality of magnets attached to the periphery of said rotary shaft; a magnetic sensor, wherein the rotating speed of said first and second feed gears (108, 109) is detected by said magnets and the magnetic sensor. a rotary shaft of said first feed gear; a plurality of magnets attached to the periphery of said rotary shaft; a magnetic sensor, wherein the rotating speed of said first and second feed gears (108, 109) is detected by said magnets and the magnetic sensor.