To precisely and automatically recognize the position of a cutting edge without removing a throw-away tip from a tool by providing a binary image data for discriminating the cutting edge part against the other part from the image data on the front of the tool.

The frequency distribution data corresponding to the tool center angle of a cutting edge picture element is formed by a frequency distribution data forming part 15. The arranging angle of the cutting edge around the tool is found by a cutting edge arranging angle calculating unit 19 from the frequency distribution data formed by the frequency distribution data forming part 15 by referring to the tool information stored in a tool information data base 17. The position of the tool cutting edge is specified by a tool cutting edge position calculating unit 21 from the cutting edge arranging angle found by the cutting edge arranging angle calculating part 19 by referring to the tool information.