PROBLEM TO BE SOLVED: To provide a machine tool having a workpiece reference measurement position setting function capable of obtaining the center coordinate of a workpiece and setting it as the workpiece reference measurement position. SOLUTION: A workpiece symmetrical to two lines in which machined surfaces are orthogonal to each other is arranged to make the axis of the mechanical coordinate system and two lines parallel to each other. A spherical measurement piece of a probe of an on-machine measurement instrument is relatively moved toward an end face of the workpiece from the top of the machining surface of the workpiece along the first line parallel to the two lines. After the spherical measurement piece is detached from the end face of the workpiece, the coordinate when the moving speed in the axial direction of the probe reaches the predetermined value is stored (S2-S11). Similarly, the coordinate is stored for the second line (S12-S21). Each mid-point is obtained from the stored coordinate. The obtained coordinate of the mid-point is the center coordinate of the workpiece, and can be set as the reference measurement position of the workpiece. COPYRIGHT: (C)2010,JPO&INPIT