To prevent pressure rise in a fluid joint due to thermal expansion of an operating fluid by arranging a fluid storage tank storing the operating fluid at a position higher than an output shaft, and communicating the fluid storage tank with an operation chamber formed of a pump and a turbine.

A fluid storage tank 60 storing an operating fluid is arranged at a position higher than an output shaft 46 fitted with a turbine 43 of a fluid joint. The fluid storage space 61 of the fluid storage tank 60 is communicated with an operation chamber 40a formed of a pump 42 and a turbine 43 via a communication path 67, a passage 462, a passage 461 and a chamber 40a formed of a casing 41 and the pump 42. Even when the operating fluid is heated and thermally expanded while circulating, the thermally expanded quantity can be absorbed by the storage space 61. The pressure increased by absorbing the thermally expanded quantity of the operating fluid is released to the atmosphere via an air breather 65, and pressure rise due to the thermal expansion of the operating fluid can be prevented.