To improve riding comfort in a state of properly filling air pressure, by improving a core body.

A run-flat tire assembly 1 has the core body 9 for supporting a load of a tire 2 when reduced in the air pressure of the inner cavity (i) surrounded by a rim 3 and the tire 2. The core body 9 includes a loading plate 10 fixed to a well 8; at least one coil-shaped elastic body 11 with only one end side fixed to the loading plate 10, extending in the tire radial direction; a fastener 12 compressing the coil-shaped elastic body 11, fixing the elastic body 11 to the loading plate 10 in a state of contracted in the tire radial direction; and a core unit 9A having a cutter 13 for cutting the fastener 12 in response to reduction in the air pressure.