To exhibit various correcting functions impossible in a linear motion mechanism by setting a cutting tool to slidingly move in the vertical direction being the parallel direction to a rotary shaft of a lapping machine, in a tip part of a rotary arm to make the circular arc motion.

A rotary arm 6 is installed on a rotary shaft 5, and a cutting tool 4 is installed in a tip part of this rotary arm 6. The rotary arm 6 is driven in turning by a driving motor part. Squareness of the rotary shaft 5 and a plane of a lap surface plate 3 is adjusted by a level adjusting mechanism 8. A tool post is arranged in the tip part of the rotary arm 6 through a slide mechanism to adjust a notch quantity. A notch quantity of the cutting tool 4 is adjusted by a micrometer. In this constitution, the cutting tool 4 is vertically moved, and the rotary arm 6 is rotated in the radial direction of the lap surface plate 3. A surface of the lap surface plate can be finely cut by adjusting rotational driving of the driving motor part and a notch depth of the cutting tool 4.