Control device for machine tool and machine tool including the control device

A machine tool comprising a workpiece holding unit for holding a workpiece, a tool post to hold a cutting tool for cutting a workpiece, a rotating unit for rotating the cutting tool and the workpiece relative to each other, a feeding unit for feeding the cutting tool and the workpiece in a predetermined feed direction, a vibration unit for reciprocally vibrating the cutting tool and the workpiece relative to each other, and a control device comprising a control section to make the machine tool machine the workpiece via the rotation of the cutting tool and the workpiece relative to each other and via the feeding of the cutting tool in the feed direction to the workpiece with the reciprocal vibration, wherein the control section determines a number of rotations of the workpiece and cutting tool relative to each other and a number of vibrations of the reciprocal vibration per rotation in the rotation of the workpiece and cutting tool relative to each other when the workpiece is machined in accordance with a vibration frequency dependent on a period in which an operating instruction can be executed.