A run-flat support body and a method assembling the same that improves reliability during running by eliminating mechanical joint components and realizes weight reduction and uniform mass-production are provided. The run-flat support body of the present invention comprises a pair of elastic rings fitted to a rim of a wheel and an annular shell bridging between these elastic rings. In the run-flat support body, the elastic rings and the annular shells are integrally joined, at least one discontinuous spot is provided in a circumference of the annular shell and the elastic rings, a connection structure is formed in which butted ends of the annular shell are joined together by welding, and joining between the annular shell and the elastic ring is partially released in the vicinity of a butted position of the annular shell. When the run-flat support body is inserted into a cavity portion of a pneumatic tire and the butted ends of the annular shell are joined together by welding, the welding work on a portion covered by the elastic ring is performed in a state where the elastic ring is retreated from the butted position of the annular shell.