To provide a core and an assembly body of a tire with a rim using the same which is disposed in a tire inner cavity and can support tire load when the tire is punctured.

The core is disposed in a tire inner cavity surrounded by the tire and the rim assembling the tire to the rim and supports load by abutting to the inner surface of a tread part only when the internal pressure of the tire drops. The core comprises an annular core body made of foam material and an outer skin part made of solid material which is fixed to the core body and abuts to the inner surface of the tread part.