A device for monitoring a mounting state of a workpiece in a machine tool. The device comprises an illumination arrangement for illuminating the working space in a normal mode of operation; at least one workpiece sensor, which is configured to detect an actual state of the workpiece in the workpiece mount in the working space, and to provide a monitoring signal which describes the actual state of the workpiece; and a control unit. The illumination arrangement is also operable in at least one signal mode of operation. The control unit is configured to determine, based on the monitoring signal, whether the workpiece is in a first mounting state or a second mounting state, and, based thereon, to selectively operate the illumination arrangement in the signal mode of operation to provide visual information in the working space for visualizing the mounting state of the workpiece.