PURPOSE: To prevent quench of field winding, by employing a liquid helium flow-out port having specific shape thereby promoting flow of liquid helium through a superconducting field winding.

CONSTITUTION: Superconducting field windings 1 of a rotor constituting a superconducting generator contain superconducting coils 1A∼1D in saddle type slots 3 provided at the outer circumferential side of a winding shaft 2, where many liquid helium inlet ports 4 penetrating through the bottom of the slot 3 and the inner circumferential side of the winding shaft 2 are made in the winding shaft 2 and an outlet port 5 is made near the end of winding. A liquid helium container 6 is fixed around the winding 1. The liquid helium outlet is made larger at a portion near to a magnetic pole where the flux density is high and decreased gradually toward the end of the winding. Consequently, flow of liquid helium through the winding is promoted.