PURPOSE: To prevent leakage of a gaseous refrigerant from the inside of a winding fixing shaft into a collector ring coupling shaft fixed to the end part shaft thereof.

CONSTITUTION: A winding fixing shaft 1 applied with a superconducting field winding 2 is arranged coaxially, on the outside diameter side thereof, with an outer tube 4 through a vacuum heat insulation layer 3. The winding fixing shaft and the outer tube are supported, at the opposite end parts thereof, by end part shafts 5a, 5b. A current lead 8 penetrates one end part shaft 5b coupled with a collector coupling shaft 6 having outer circumferential face fixed with a collector ring 11 which is connected through a stud with the outside end of the current lead 8. Furthermore, a hermetic seal 13 is provided between the current lead and one end part shaft. In such superconducting rotor, a gas chamber 16 isolated from the outside of the machine is formed in the collector coupling shaft 6 by hermetically sealing 14 the gap between the stud 10 and the through hole of the collector coupling shaft 6 and a gas excellent in breakdown strength is encapsulated in the gas chamber.