A superconducting power transmission system that comprises an inner pipe housing a superconducting cable therein, a radiation covering at least a part of the inner pipe from outside; and an outer pipe housing the inner pipe and the radiation shield therein. A vacuum is created in a space from an inside of the outer pipe to an outside of the inner pipe with the radiation shield therebetween. The system further comprises at least one radiation shield pipe, housed in the outer pipe and thermally coupled with the radiation shield, a liquefied natural gas (LNG) as a second cryogen for the radiation shield being made to flow through the radiation shield pipe.