PURPOSE: To enhance the transmitting efficiency of driving torque to a belt, transmit a high torque with a small power to enhance the working speed of cutting or polishing, quietly perform the working in the sound suppressed state, improve the belt life of a saw tooth, and facilitate the unmanned control.

CONSTITUTION: An endless belt-like saw tool 1 is laid over two pulleys 2, 3 and driven by rotation. As its driving device, driving motors 4, 5 are provided on both the pulleys 2, 3, respectively. They are belt driving devices for transmitting a high driving torque to the belt 1 as power vehicles. The circumferential surfaces of the pulleys 2, 3 making contact with the saw tooth 1 is subjected to the treatment for enhancing the frictional coefficient to prevent a slip, so that the power transmitting efficiency is enhanced. As the power vehicle, the device is formed by use of a low specific gravity material, and a high hardness material is adhered to the surface.