The present invention provides a run-flat support body and a tire/wheel assembly whose weights can be respectively reduced. The run-flat support body includes an annular shell and elastic rings, the annular shell having an outer peripheral side as a support surface and an inner peripheral side formed in fork-shaped open legs, the elastic rings being attached respectively to the legs portions of the annular shell, and the elastic rings being designed to be mounted on a rim of a wheel. The annular shell is formed of a porous structural material having fine voids. The run-flat support body is attached to an inside of a pneumatic tire mounted on the rim of the wheel.