Problem to be solved: to provide a technique for obtaining information about tool edge.The control section 20 moves the cutting tool 11 relative to an object having an arcuate surface having a known shape, and the coordinate value of the contact sensor 11 when the cutting edge of the arc of the cutting tool 11 comes into contact with the arcuate surface of the object is detected by the contact sensor A function is obtained by using the time series data of the detected values relating to the drive motor included in the rotation mechanism 8 and / or the feed mechanism 7.The control unit 20 obtains at least one of the nose radius of the tool edge, the central coordinate of the tool edge, and the shape error of the tool edge, based on the coordinate values when the cutting edge of the arc of the cutting tool 11 and the arcuate surface of the object contact each other at least three different positions.Diagram
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