To always put a probe into contact with a correct reference surface by providing a head with a probe which is in contact with the upper surface of a work and is freely rotated around a cutter.

A head 10 and a cutter 15 is moved along a foreign material 43 by a command from an NC control device to cut away a projection and a flash 44a of the foreign material 43. A probe 27 is moved by a turning motor 25 along the surface 41a of a main board 41 in the inner side of the foreign material 43. If a part of the surface 41a is wavy in up and down directions, the probe 27 is moved up and down and a detector 33 detects up-and-down movement amount to send it to a driving circuit 35 of a servo motor 5, thereby turning a Z-axis servo motor regularly or reversely to move up and down the head 10 in response to the amount of the up-and-down movement of the probe 27. The cutter 15 is held at a constant height for the surface 41a of the main board 41 to cut away the projection and the flash 44a of the foreign material 43.