A control device for a machine tool that moves a tool relative to a workpiece and/or vice versa and machines said workpiece. Said control device is provided with a display unit that displays information related to the machine tool, a first-layer generation unit that generates a first layer that contains machining information related to the machining being performed on the workpiece, and a second-layer generation unit that generates a second layer that contains an image or handwritten note related to the machining information in the first layer. The display unit displays an image consisting of the second layer superimposed onto the first layer.