PURPOSE: To improve dynamical unbalance of transmission torque around a center line as the rotational center as well as to easily and inexpensively constitute a power transmitting device into a compact size by which transmission torque is increased according to the relative rotational speed.

CONSTITUTION: Pump gear pairs 16, 18, 20 for performing the pump action by the relative rotation of an input shaft 12 and an output member 14 are arranged around a center line O by being deviated by the angle of 120°C. Partition plates 54 arranged on both sides of respective pump gear pairs 16, 18, 20, and for forming pump chambers are provided with the specified clearances between the pump gear pairs 16, 18, 20, pressure of silicone oil is increased by the flowing resistance in flowing of high-viscous silicone oil according to the relative rotational speed, and the transmission torque between the input shaft 12 and the output member 14 is therefore increased according to the relative rotational speed.