To reduce a drug torque without reducing a transmitting torque by including an impeller of a pump to a rotational direction downstream side from a diameter direction inner end toward a diameter direction outer end.

In a fluid coupling, since an impeller of a pump 41 is inclined to a rotational direction downstream side of the pump 41 from a diameter direction inner end toward a diameter direction outer end, flow out speed v2 of a working fluid from the pump 41 is slightly reduced more than flow out speed from a pump in a fluid coupling wherein an impeller is formed in a straight radially. In a runner of a turbine, a torque T1' slightly smaller than a torque T1 is received from the working fluid, and the torque T1 is transmitted to the turbine. The working fluid which flows out in an arrow direction with speed v1 from the turbine, flows into the pump 41. In the case where circumferential direction speed of the working fluid which flows into the pump 41 is accelerated to speed v2x, the torque T1' is applied to the pump 41. It is thus possible to ensure a high transmitting torque, and it is also possible to reduce a drug torque.