A detector detects the state of load of machine, for example, the torque load of the spindle or the cutting resistance of the tool. Control means connected to the detector compares the detected load with an allowable magnitude and moves the tool away from the workpiece in a specific direction to reduce the load when the detected load exceeds the allowable magnitude thereby providing cutting of the workpiece by the tool at a state of load maintained at a magnitude very close to the allowable magnitude by not exceeding such magnitude.
