The invention relates to a resin composition that has, as a raw material, a product that is obtained by addition reacting a compound having a unsaturated carbon bond to a resin decomposed product obtained by chemically decomposing a urethane resin, alternatively, by decomposing a urethane resin with a compound having a unsaturated carbon bond. The resin composition can be solidified by polymerization by use of a cross-linking agent and an addition polymerization initiator. Furthermore, when a compound having two or more carboxyl groups or an anhydride thereof is blended together with the urethane resin decomposition, a resin composition can be obtained. When the resin composition obtained thereby is cured, a recycled resin with excellent properties can be obtained.