PURPOSE: To stop a cutter from piercing a work at its minimum by detecting the displacement of a contact shoe and providing an external operating means which positively displaces a corresponding interval to the contact shoe, in a detecting means.

CONSTITUTION: A detecting means C which detects the displacement quantity of a contact shoe 19 and outputs a detecting signal in a compliance with the displacement quantity gives an actuating lever 29 a rotation tendency of clockwise by the action of its dead weight and a plate spring 36. In addition, a mounting rod 38 in the lifting and lowering directions, contact pieces 39, 40 corresponding to the other end of the actuating lever 29 and a pneumatic cylinder 41 are provided. When the contact shoe 19 is disconnected from a model M and falls to a downward end rapidly, the detecting means C detects the displacement and moves a processing head downward. When the actuating lever 29 reaches the position of the contact piece 40, it rotates clockwise resisting the plate spring 36. By this action, the detecting means C moves from a definite position to downward so as to shorten an interval. The interval is made to be a defined distance, and thereby a lifting and lowering motor stops rotating so as to stop a cutter from piercing a work.