A superconductor cooling system has: a first superconductor; a first cooling conductor used for cooling the first superconductor; a first cooling unit configured to cool the first cooling conductor to a first temperature; and a current lead configured to supply a current to the first superconductor. Here, a part of a path of the current is formed of a second superconductor. The superconductor cooling system further has: a second cooling conductor used for cooling the second superconductor; a second cooling unit configured to cool the second cooling conductor to a second temperature; and a first thermal conduction switch connected between the first cooling conductor and the second cooling conductor to ON and OFF heat transfer between the first cooling conductor and the second cooling conductor.