To prevent a working fluid from being heated to high temperature.

A control valve 29 is provided on an outlet passage. The control valve 29 comprises a valve element 31 slidably provided in a spool hole 30, a first urging means 32 to urge the valve element 31 to the opening position side butted to a bottom part of the spool hole 30, and a second urging means 33 to urge the valve element 31 to the closing position side butted to a stopper 34. The spool hole 30 is formed parallel to the axis of rotation. The second urging means 33 is formed of a shape memory alloy. The second urging means 33 shrinks when the temperature of the working fluid is below a specified valve closing temperature, and the valve element 31 is located at the opening position to permit the outlet passage to open. The second urging means 33 is expanded when the temperature of the working fluid is above a specified valve closing temperature, moves the valve element 31 to the valve closing position against the urging force of the first urging means 32 to close the outlet passage.