An incremental or absolute rotation encoder with a clamping device for connecting the encoder shaft to the drive shaft of a drive unit by means of a radial clamping action. A clamping element with a first sliding surface which is inclined relative to the axis of the encoder shaft is provided resting against a corresponding second inclined sliding surface at the end of the encoder shaft facing the connection with the drive shaft. An actuating element is capable of acting on the clamping element in axial direction. Since the two inclined surfaces rest slidingly on each other, the clamping element and the end of the encoder shaft are pressed in opposite radial directions against the drive shaft.