To face the polished position of a tip to a cut position and polish the position of a tip of poor sharpness automatically without changing the working position of the tip or changing the chip itself by a worker when the sharpness of one part of the tip is lost.

This device is provided with a tip 17 with a circular section installed rotatably on the corner of an arm 3 as a tip holder and a polishing means 25 installed in a pres-contact state for at least one edge of the cutting surface 41 of the tip 17. A plate 23 fixed on the arm 3 is provided in the cutting surface side of the tip 17 and the means 25 may be fixed on the tip 17 side surface of the plate 23. A means press-contacted the means 25 to at least one edge of the cutting surface 41 of the tip 17 by energizing the plate 23 to the arm 3 side may be provided.