A thermoplastic resin composition comprising: ▪70 to 95 mass% of a thermoplastic resin; and 5 to 30 mass% of a multilayer structure polymer having a multilayer particle structure, wherein the multilayer structure polymer has a median diameter Da of no less than 200 nm and less than 500 nm when the median diameter Da is measured by a laser diffraction/scattering technique with the thermoplastic resin composition dissolved in acetone, wherein the multilayer particle structure includes an inner layer and an outer layer covering the inner layer, the multilayer structure polymer is a graft copolymer having a cross-linked rubber polymer component and a polymer component that is graft-bonded to the cross-linked rubber polymer component, the cross-linked rubber polymer component includes, as a primary component, an acrylic acid alkyl ester unit having an alkyl group with a carbon number of 1 to 8, the cross-linked rubber polymer component forming the inner layer, and the polymer component contains 80 to 97 mass% of a methyl methacrylate unit and 3 to 20 mass% of an acrylic acid ester unit, the polymer component forming the outer layer, wherein when a ratio of a mass of the graft-bonded polymer component to a mass of the cross-linked rubber polymer component is a graft rate of the graft copolymer, the graft rate is 11 to 33 mass% wherein a proportion of the polymer component relative to 100 mass% of the multilayer structure polymer is 10 to 25 mass%, and wherein when a median diameter of the multilayer structure polymer measured by a laser diffraction/scattering technique in water is a median diameter De, the multilayer structure polymer satisfies the following expression. 1.1 < Da / De ≤ 2.0 ▪70 to 95 mass% of a thermoplastic resin; and 5 to 30 mass% of a multilayer structure polymer having a multilayer particle structure, wherein the multilayer structure polymer has a median diameter Da of no less than 200 nm and less than 500 nm when the median diameter Da is measured by a laser diffraction/scattering technique with the thermoplastic resin composition dissolved in acetone, wherein the multilayer particle structure includes an inner layer and an outer layer covering the inner layer, the multilayer structure polymer is a graft copolymer having a cross-linked rubber polymer component and a polymer component that is graft-bonded to the cross-linked rubber polymer component, the cross-linked rubber polymer component includes, as a primary component, an acrylic acid alkyl ester unit having an alkyl group with a carbon number of 1 to 8, the cross-linked rubber polymer component forming the inner layer, and the polymer component contains 80 to 97 mass% of a methyl methacrylate unit and 3 to 20 mass% of an acrylic acid ester unit, the polymer component forming the outer layer, wherein when a ratio of a mass of the graft-bonded polymer component to a mass of the cross-linked rubber polymer component is a graft rate of the graft copolymer, the graft rate is 11 to 33 mass% wherein a proportion of the polymer component relative to 100 mass% of the multilayer structure polymer is 10 to 25 mass%, and wherein when a median diameter of the multilayer structure polymer measured by a laser diffraction/scattering technique in water is a median diameter De, the multilayer structure polymer satisfies the following expression. 1.1 < Da / De ≤ 2.0