A clamping device for machine tools with a power-operated chuck, the clamping jaws of which are actuatable by the clamping device via a movement converter and draw rod. A drive motor is provided with a switching element which is adjustable by axial control in a middle and two limit positions, wherein the switching element is connectable to the clamping device in one limit position and, in the other limit position, to an adjustment element connectable to an auxiliary device. The switching element is lockable in the limit positions with a machine spindle. The clamping device is thereby provided with an increased range of applications, without functions being impaired, with little structural complexity, because the switching element makes possible a clamping element integrated in the power operated chuck to be operated using the drive motor, such that further procedures can be undertaken without changing the clamping device.