To apply different engaging forces to two friction clutches by one and the same actuator.

A clutch mechanism is composed of friction clutches 3, 5, gear assemblies 11, 13, cams 17, 19 provided to output gears 35, 37 in the gear assemblies 11, 13 and adapted to be operated by relative rotation in different directions, respectively, so as to press the friction clutches 3, 5, respectively, a pressure receiving member 21 for supporting one of the output gears 25, 37 when the other one of the gears presses the associated friction clutch, and a reversible motor 15 for rotating the gear assemblies 11, 13 so as to relatively rotate the output gears 35, 37 in different directions in order to actuate the cams 17, 19.