PURPOSE: To aim at improvement of efficiency of a fluid coupling by providing a temperature regulating valve for regulating flow quantity at an operating oil inlet according to the temperature of oil at an operating oil outlet in an operating oil inlet circuit and supplying necessary circulating oil quantity to a closed circuit according to slippage loss during operation.

CONSTITUTION: A temperature regulating valve 8 opens or closes a passage in a valve 8 according to the temperature of operating oil in a closed circuit to regulate oil quantity flowing in the closed circuit in optimum circulating oil quantity. A solenoid valve is closed only at the time of starting and is opened at the time of normal operation. When the valve 8 restricts the passage to rise pressure in the circuit the pressure regulating valve 10 is opened to maintain pressure in the closed circuit constant. A fluid coupling consists of a impeller 12, a runner 13 and a operating chamber 14. The position of a scoop pipe 16 is adjusted in the axial direction to scoop operating oil 15 in the operating chamber 14 for regulating the oil quantity thereof and the rotating speed N2 of the runner can be adjusted relative to the rotating speed N1 of the impeller 12. Consequently, necessary circulating oil quantity can be supplied according to slippage loss during operation.