A phase split structure of a superconducting cable includes three cable cores each having a shield layer provided around a superconductor, a splitter box housing the three cable cores extending from an assembly portion where the three cable cores are assembled into the cable, in a state in which the cable cores are spaced apart from each other, and an electrically-conductive connecting portion connecting respective shield layers of the cable cores to each other within the splitter box. In this way, occurrence of a large magnetic field outside the cable cores can effectively be reduced.