Abstract: A numerically controlled machine tool such as a roll grinder grinds a workpiece into a roll shape by rotating the workpiece about its own axis at a prescribed speed, and moving a grinding tool in radial and axial directions of the workpiece. The machine tool has a first motor for rotating the grinding tool about its own axis and a second motor for moving toward and away from the workpiece in the radial direction thereof. The machine tool also includes a detector for detecting a drive current supplied to the first motor, and a control unit for comparing the value of the drive current detected by the detector and a preset current value and for controlling the second motor based on the result of comparison.