To provide a torque converter capable of varying a torque capacity τ even at the time of sudden acceleration during traveling of a vehicle.

In this fluid coupling, an opening part 17 connecting the inside and outside of a turbine shell 7 is formed, an opening and closing mechanism 18 for opening and closing the opening part 17 by a difference in oil pressures of hydraulic fluid in a pump impeller 2 and hydraulic fluid in a turbine runner 6 is provided, and when the difference in the oil pressures of the hydraulic fluid is large, the opening part 17 is opened and the hydraulic fluid in the turbine runner 6 is discharged to the outer peripheral side of the turbine shell 7. When an input torque TEGwith respect to the torque converter 1 is increased from a driving power source at the time of starting or sudden acceleration of the vehicle, the torque capacity τ of the torque converter 1 can be made small, and rising of a rotational speed NEGof the driving power source can be improved. As a result, startability and acceleration performance of the vehicle can be improved.

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