PURPOSE: To prevent thermal leak, by arranging coils inside and outside a vessel accommodating a superconducting machine, and receiving and delivering electric power thorough the electromagnetic coupling of both coils.

CONSTITUTION: A superconducting generator 1 and an electric power converter 3 in an insulator vessel 2 are connected with leads 7, and the output of the converter 3 generates AC output. This output is delivered to a winding 15 wound around a U-shaped magnetic belt 4. As a result, magnetic flux generated by the current flowing through the winding 15 penetrates the vessel 2, flows into an external magnetic belt 5, and generates electromotive force in an output winding wound in the same manner. This is converted to electric power of necessary frequency or voltage by the electric converter 6, and output on leads 8. Thereby a connector with little thermal leak can be obtained.