A control device for a machine tool for machining a workpiece while orbital movement is performed for causing an auto-rotating rotary tool to move in a circular manner, the control device comprising: a reading and interpreting unit for reading a machining program containing input information; and a computing unit for combining a first tool pathway along which a rotary tool travels and which has been set on the basis of input information about the travel of the rotary tool, and a second tool pathway along which the rotary tool orbits and which has been set on the basis of input information about the orbital movement, and for setting a third tool pathway along which the rotary tool travels in a machining shape while moving in an orbital manner.