PURPOSE: To enhance the reliability and the safety of a superconducting rotor by disposing a heat insulating wall having small thermal conductivity between the torque tube of an inner cylinder and liquid helium.

CONSTITUTION: In a superconducting rotor, an axial liquid helium passage 13 is formed in a gap between a wedge 13 of the bore side of the coil slot 11 of a coil cylinder 2 and a torque tube 2a, and a liquid helium peripheral passage 14 is formed on the outer periphery of the cylinder 2. The passages 13, 14 form a groove-shaped heat-insulating wall 15 and a square-sectional cylindrical circular arc-shaped heat-insulating wall 15a of a material such as fluorine resin, carbon, etc., having small thermal conductivity under low temperature condition to prevent liquid helium 16 from direct contact with a structural member. Thus, even if an eddy current loss occurs on the surface of a low temperature danger 9 due to 3-phase short-circuit, the walls 15, 15a are disposed between a high temperature member and a low temperature liquid helium. Thus, a time required for a heat transfer is sufficiently long to eliminate an abrupt internal pressure rise.