PURPOSE: To perform cutting edge angle adjusting work accurately and in a short time by automatically changing the end cutting edge angle of a cutting tool in a proper angle range while in cutting and, moreover, by adjusting it so as to become a proper end cutting edge angle with correspondability with surface roughness and the variable range of the cutting edge angle.

CONSTITUTION: After the surface roughness of a workpiece 10 is measured after cutting the workpiece 10 with the end cutting edge angle of a cutting tool 4 varied continuously while in performing ultra precision cutting, and the end cutting edge angle which excellent surface roughness may be obtained thereby is calculated from the resultant surface roughness and a cutting position, an end cutting edge angle adjusting device is started by driving an angle adjusting motor 8. On the top of a feed slide a cross slide is placed, and a cutting tool 4 is secured to the end cutting edge angle adjusting section 3 on the top of the feed slide through a clamp 5. The end cutting edge angle adjusting section 3 is engaged to a swivel center shaft 6 and swiveled through a worm gear 9 rotated by the angle adjusting motor 8. This leads to the formation of an angle adjusting device 7 including an encoder 8' that is a position detector for controlling, which enables the read out of swivel angles.