PURPOSE: To cut a work straight, by continually detecting the direction of a guide and performing a necessary control of an attitude for a strip-shaped saw blade when it cuts the work.

CONSTITUTION: A base 14 forms its peripheral part concentrically with the internal periphery, that is, in a circular shape with the point end of a saw blade 1 serving as the center. A sensor base 18 performs rotary motion with said base 14 serving as a guide, and side surfaces of the saw blade 1 are held between a pair of guide pads 11, 12 in the central part of the sensor base 18. a change of attitude of the saw blade 1 is converted into the rotary motion of the sensor base 18, and a movement of its mounted sensing piece 19 is detected by sensors 20. A motor 16 is rotated by electrically processing a signal from the sensors 20, and the saw blade 1 is changed into a proper attitude by an electric control circuit.