PURPOSE: To improve a work efficiency and to increase reliability, by arithmetically processing an approach distance with its operation, quick-approaching the approach distance, based on a detection value, and performing cutting by changing over to a cutting speed just before a tool being brought into contact with a work.

CONSTITUTION: When a work W is pressed by a work pressing device 25, after clamping the work W, the approach distance until a tool T is brought into contact with the work W is arithmetically processed by an arithmetic process device 69, based on the detected value detected by a 1st position detecting device 25a and that detected by a 2nd position detection device 15a, and stored in an approach distance/memory 71. Now, when the tool T is approached to the work W at the approach speed from a set position by a driving device 29, the actual detection value of the 2nd position detecting device is changed in order, the change quantity of this detection value and a stored approach distance are discriminated with their comparison by a comparison discriminating device 73, the change quantity is commanded so as to change over to a cutting speed from the approach speed to a speed changeover device 31, when it becomes almost equal to the approach distance.