To prevent acceleration to an overspeed condition of a constitutional element in a hydraulic power transmitting device.

In a hydraulic power transmitting device 11, 12 provided with a variable displacement pump 13, 14 and fixed displacement pump 16, 17 driven by an engine 18, an overspeed control device 10 is provided. In the overspeed control device 10, when a rotational speed of the engine 18 exceeds a prescribed level, a hydraulic pressure level of a capacity control device 24, 26 is reduced, during the time the variable displacement pump 13, 14 are operated as a motor, a capacity of the variable displacement pump 13, 14 is reduced, brake torque of the engine 18 is increased.