PURPOSE: To prevent an inferior pattern from being formed by a method wherein a means for detecting an abnormality concerning a cutter is provided and a control means by which a required treatment is performed when the abnormality is detected, is established.

CONSTITUTION: An electrode 5 is so provided as to be in contact with a root of a cutter 3 and another electrode 7 is respectively so provided as to be in contact with a top of the cutter 3. When the cutter 3 is normal, an electrification path is formed by a path of the electrode 5 - the cutter 5 - the electrode 7. On the contrary, when abnormalities such as failure or the like concerning the cutter 3 exist, no electrification path is formed. When an abnormality detection part 1 detects the abnormality, the abnormality detection part 1 has a control function for executing necessary processing such as interrupting cutting, informing an operator of the point together therewith, etc.