Abstract: The invention relates to an arrangement for automatic control of a hydraulically operated friction disc clutch with diaphragm spring. The hydraulic operating unit comprises a hydraulic cylinder which, by acting on the diaphragm spring, disengages the friction disc clutch. In order to obtain a hydraulic operating unit in which the regulating pressure is proportional to the disengagement degree of the clutch, the hydraulic cylinder comprises a proportionality-forming spring which acts against the hydraulic cylinder piston during the final part of the disengagement stroke of the piston. In a system with master cylinder and slave cylinder, where the slave cylinder acts on the diaphragm spring for disengagement of the friction disc clutch, the master cylinder is also provided with a pressure supply, compensating for wear of the discs, via a hydraulic channel which is closed off at a predetermined regulating pressure level.