A clutch device for a vehicle, comprising a spring device (4), which attempts to force a friction plate (3) in a first direction for engagement of the clutch, a pneumatic actuator (10) with a cylinder (11) and a piston (16), which divides the cylinder (11) into a main chamber (20) and an auxiliary chamber (21), and a compressed air source (31), which is arranged via a controllable valve device (32,33) for communication with the main chamber (20) for movement of the friction plate (3) in a second, opposite direction for disengagement of the clutch. The clutch device comprises a computer (50) with a memory (54), wherein there is stored a desired auxiliary force exerted against the release bearing (19) as a second function (C2) of the release bearing's (19) position. The clutch device further comprises a sensor (22), which is arranged to establish the release bearing's position, and a sensor (23), which is arranged to establish the pressure of the air in the auxiliary chamber.The valve device (36) can connect the compressed air source (31) with the auxiliary chamber (21), and the computer (50) can receive signals from the sensors (22,23), establish any difference between the measured auxiliary chamber pressure and the desired auxiliary chamber pressure and control the valve device (32,33,36) in accordance with the difference and thereby provide the auxiliary force.