PURPOSE: To provide a rotor of a highly reliable and safe superconducting rotary electric device which can prevent excessive rise of pressure by quickly releasing a coolant if an interior pressure of rotor rises.

CONSTITUTION: A coolant exhaust pipe 15 to exhaust liquid helium 10 is provided at the outside of a rotor and a solenoid valve 17 is provided at a stationary portion of the coolant exhaust pipe 15. Meanwhile, a solenoid valve is also provided at the stationary portion of a coolant supply pipe 9 to supply the liquid helium 10. In any one of the solenoid valves 17, 20, its opening and closing condition is detected automatically with a pressure sensor provided within a cylinder in the rotor by setting an allowable pressure value with a controller 19 provided in the stationary portion. Thereby, the liquid helium 10 in a low temperature rotor 2 is released to the outside or supply of the liquid helium 10 is stopped.