PURPOSE: To decide the state of the wear and breakdown of a tool after completion of each work and to perform the stoppage and earing of a machine, the display of the work data up to the present, etc., by storing and operating a cutting power at the work stage simultaneously with performing the detection of the wear and breakdown of a tool during working.

CONSTITUTION: A small power detecting device 17 detecting the power of a main shaft motor 4 or feed motor 11 is installed, the output thereof is digitized via a digital meter relay 18 and the numerical value conformed to the wear or breakdown of each tool is stored to the set value of the digitalmeter relay 18 in advance. The output from the small power detection device 17 and set value are compared, a machine is stopped in case of exceeding the set value and in case of not exceeding the maximum value is transmitted to a wear and damage detection controller 20 via a comparator 21 after completion of each work. The wear and damage detection controller 20 decides the wear and breakdown by comparing and studying the maximum value of a storing work power, outputting the command of the machine stoppage, etc., to a numerical control device 15 and control panel 16.