To provide a fluid gearing with a lock-up clutch capable of generating the maximum engine torque at the time of starting-up and improving drivability.

The fluid gearing has a lock-up clutch 30 which is arranged in parallel on a power transmission route between a pump impeller 11 and a turbine runner 13 of a fluid coupling 10 arranged between a driving side and a load side and changes the power transmission route, and determines a stall capacity coefficient Cs (N*m/rpm2) on the basis of the number of engine rotations for generating the maximum engine torque Tmax at the driving side, and transmits the rotation at the driving side to the load side thereby. Thus, the best accelerating performance can be obtained by setting the stall capacity coefficient Cs so as to make the number of stall rotations reach near the number of rotations for the maximum engine torque, drivability can be improved by setting at a level of a controlled amount wherein there is no sense of incompatibility between an amount of stepping on an accelerator and speed of a vehicle, and its fuel consumption can be also improved.