To measure only abrasion of a tool by removing thermal displacement of a machine and an effect of vibration of the tool from variation of a cutting-edge position of the rotating tool.

The cutting-edge 102 of the tool shields a laser beam 35 to vary a light receiving amount, and a projection amount of the cutting-edge is measured using the tool cutting- edge position detector for detecting a tool's cutting-edge position based on the variation of the light receiving amount. The tool is moved from a state I where the tool does not cross the laser beam 35 to a state II where the cutting-edge 102 intermittently shields the laser beam 35, and a tool position when the light receiving amount varies, namely a first detection coordinate Zc, is detected. Next, the tool is moved from a state I' where the tool core 103 perfectly shields the laser beam 35 to a state II' where the cutting-edge 102 intermittently shields the laser beam 35, and a tool position when the light receiving amount varies, namely a second detection coordinate Zb, is detected. The projection amount of the cutting- edge is calculated based on a difference between the first detection coordinate Zc and the second detection coordinate Zb. The projection amounts of the cutting-edge are measured before and after machining by the tool, and a tool abrasion amount is calculated based on a difference between them.