PURPOSE: To miniaturize a transmission torque characteristic changing actuator by disposing, on the outer circumference of a third rotating shaft, a cylindrical sleeve having a fluid channel formed in an outer circumferential surface position possible to communicate with a discharge oil passage having an orifice.

CONSTITUTION: When a relative rotating speed difference is formed between first and second rotating shafts 24, 22, the flow rate discharged by the operation of a piston 50 according to this is converted into a fluid pressure by the orifice 71 provided on the oil passage 70 of a rotor 40 and further into a transmission torque between the both shafts. When a motor actuator 91 is driven by a determined control command, a cylindrical sleeve 90 disposed on the outer circumference of a third rotating shaft (left front drive shaft) 4 conducts stroke, and the relative position between the fluid channel 72 on its outer circumferential surface and the orifice 71, or the orifice opening area is changed, whereby the transmission torque characteristic can be changed. Hence, miniaturization of the actuator, reduction in torque fluctuation, and reduction is distribution of the characteristic every unit can be achieved.