An electric rotary machine (for example, a dynamoelectric machine) having a superconducting rotor is disclosed in which an outer shielding member for protecting a superconducting field winding from the influence of the magnetic flux from the stator side and for interrupting heat radiated from the normal temperature side is made of a nickel alloy containing not more than 0.3% carbon, not more than 1% silicon, not more than 2% manganese, not more than 1.5% titanium, from 2 to 8% aluminum, from 8 to 40% copper, and not less than 55% nickel for the balance by weight. The nickel alloy has a structure that a .gamma.'-phase precipitation is formed by aging in an austenitic matrix, and is non-magnetic at 20.degree. C.