PURPOSE: To enable highly reliable drill life judgment during the operation of a machine to be conducted by detecting a cutting torque, a cutting thrust, and a vibration due to cutting to obtain drill cutting information and judging the cutting conditions of a drill by processing these data complexedly.

CONSTITUTION: A detector 4a is installed on a control device 4, and a power consumption of a spindle motor 3 and a feed motor in Z-axis direction is measured. Also a vibrometer is installed on a spindle 2, a vibration signal during cutting is detected by a detector 7, its signal (V) is processed by an FFT8, and a vibration data V for which a threshold value is set is input into a complex analytical processing device 10. On the other hand, a power consumption of the spindle motor 3 and the feed motor in Z-axis direction is a function of cutting torque and cutting thrust. They are taken out by the detectors 5 and 6, respectively, and input into the processing device 10 as torque data T for which a threshold value is set and thrust data S. Then these three types of data are averaged for use in judgment of drill life.