Disclosed is a thermoplastic resin composition containing a graft material and an organic peroxide group dispersion medium in which the graft material is dispersed. The graft material is obtained by melt-mixing a metal oxide fine particle having an organic peroxide group on the surface and a thermoplastic resin, and has a structure in which the thermoplastic resin is grafted to the metal oxide fine particle. The organic peroxide group on the surface of the metal oxide fine particle is preferably a peroxymonocarbonate group. The organic peroxide group on the surface of the metal oxide fine particle is preferably obtained by reacting a hydroxy group of a silicon oxide fine particle with an amino-modified silane coupling agent, thereby introducing an amino group to the surface of the silicon oxide fine particle, and then reacting the amino group with a compound having an ethylenically unsaturated group and an organic peroxide group.