In a clamping device for a machine tool, the machine tool is provided with a power-operated chuck, and the clamping device is provided with an electrical drive motor, and a movement converter, with a force accumulator. An output element is rotatably mounted on the output shaft of the drive motor, and is in fixed driving connection with the movement converter. The output element is adapted to be connected to the output shaft by a first servo device, and the movement converter can be interlocked with the spindle of the machine tool by a second servo device. The structure enables the energy to be supplied to the clamping device for making it possible to clamp or unclamp a workpiece. During working procedures, the drive motor is stopped. There is no need for elaborate control functions, rather the servo devices are actuated to make a driving connection between the drive motor and the movement converter, or to release this connection, and to block the movement converter during working procedures by means of its connection to the spindle of the machine tool.