Provided is a thermoplastic resin having excellent thermal conductivity, in which thermoplastic resin a change in number average molecular mass caused by progress of polymerization occurring when the thermoplastic resin material is melted and a change in thermal conductivity caused by the change in number average molecular mass are low. The thermoplastic resin has (A) a specific structure and (B) ends of molecular chains sealed by a monofunctional low molecular weight compound. The resin itself has excellent thermal conductivity. The change in number average molecular mass becomes small during melting of the thermoplastic resin material, so that the change in thermal conductivity of the resin itself becomes small.