PURPOSE: To quickly discharge coolant gas from a machine if the gas pressure is extraordinarily increased within its rotor, and keep on preventing increase in heat.

CONSTITUTION: A rotor for superconducting electric rotating machines is constructed as follows: Its winding installing shaft 1 has a hollow portion 3 for storing coolant liquid at its center, and has superconductive field winding 2 installed around it. A coolant discharging path that connects to the inside of the winding installing shaft at its one end and that extends toward the center shaft, is formed. The coolant discharge path is so designed that coolant gas produced in the hollow portion in the winding installing shaft will be let out of the rotor through an exhaust hole formed at the end of the shaft. To this end, two safety valves 9a, 9b are formed in the coolant discharge path. One 9a of the safety valves is placed on the low temperature side of the portion connecting the coolant discharge path and the hollow portion in the winding installing shaft. A vacuum exhaust pipe 14, extending to the atmosphere in the radial direction, is formed between the two safety valves, and a gate valve 15 is placed in the exhaust pipe 15. In normal operation, the space defined by the two safety valves 9a, 9b and the gate valve 15, is kept in vacuum.