PURPOSE: To installing a band saw tooth automatically by providing a saw-tooth passage, a saw-tooth suppling means, a saw-tooth carring means, a flash butt welding means and a polishing means, and stretching a band saw tooth over a driving wheel and a driven wheel,

CONSTITUTION: A band saw tooth 21 is supplied to a saw-tooth passage 31 through a saw-tooth suppling part 39 to be carried by a saw-tooth suppling and carrying means 41 along the passage 31. At this stage, when the saw-tooth 21 having the predetermined length is supplied to the saw-tooth supplying part 39 through a measuring roller 49, the saw-tooth 21 is cut by the cooperative movement of cutters 53a, 55a of a cutting device 51. Next, one end of the saw-tooth 21 is held by a clapping device 59 under the condition that it is projected to right at the predetermined length, and the other end of the saw-tooth 21 is held by the clamping device 63 under the condition that it is projected to left at the predetermined length. Next, when a large current is flown to saw-tooth guides 25, 27 to contact one end of the saw-tooth 21 to the other end thereof, a contact part is heated concentlately, and they are welded when the temperature of the contact part reach the optimum temperature. Then, the saw-tooth 21 is flash-welded to be the endless condition. A grinding wheel 95 is rotated to polish a burr of the upper side of the welded part of the saw-tooth 21.