A resin composition comprising: polymer particles I, each having a three-layered structure composed of an innermost layer made of a rigid polymer c comprising 80 to 100% by mass of a methacrylic acid ester unit, an intermediate layer made of a soft polymer i comprising 40 to 99.9% by mass of an acrylic acid ester unit and 0.1 to 5% by mass of a poly-functional monomer unit, wherein the soft polymer i has a glass transition temperature of less than 25°C, and an outermost layer made of a rigid polymer o comprising 80 to 100% by mass of a methacrylic acid ester unit, wherein the polymer particles I have a weight-average molecular weight of an acetone soluble-matter of 70,000 to 100,000 and a volume average particle diameter determined by a light-scattering method of 150 to 300 nm; and polymer particles II, each having a single-layered structure composed of only a layer made of a rigid polymer s comprising 80 to 100% by mass of a methacrylic acid ester unit, wherein the polymer particles II have a weight-average molecular weight of an acetone soluble-matter of 60,000 to 90,000 and a volume average particle diameter determined by a light-scattering method of not more than 150 nm, wherein a mass ratio of the polymer particles I relative to the polymer particles II is 55/45 to 75/25, and the weight-average molecular weight of the acetone soluble-matter in the polymer particles II is smaller than the weight-average molecular weight of the acetone soluble-matter in the polymer particles I by not less than 5000, and wherein the glass transition temperature and the weight-average molecular weight of an acetone soluble-matter are determined as described in the description. polymer particles I, each having a three-layered structure composed of an innermost layer made of a rigid polymer c comprising 80 to 100% by mass of a methacrylic acid ester unit, an intermediate layer made of a soft polymer i comprising 40 to 99.9% by mass of an acrylic acid ester unit and 0.1 to 5% by mass of a poly-functional monomer unit, wherein the soft polymer i has a glass transition temperature of less than 25°C, and an outermost layer made of a rigid polymer o comprising 80 to 100% by mass of a methacrylic acid ester unit, wherein the polymer particles I have a weight-average molecular weight of an acetone soluble-matter of 70,000 to 100,000 and a volume average particle diameter determined by a light-scattering method of 150 to 300 nm; and polymer particles II, each having a single-layered structure composed of only a layer made of a rigid polymer s comprising 80 to 100% by mass of a methacrylic acid ester unit, wherein the polymer particles II have a weight-average molecular weight of an acetone soluble-matter of 60,000 to 90,000 and a volume average particle diameter determined by a light-scattering method of not more than 150 nm, wherein a mass ratio of the polymer particles I relative to the polymer particles II is 55/45 to 75/25, and the weight-average molecular weight of the acetone soluble-matter in the polymer particles II is smaller than the weight-average molecular weight of the acetone soluble-matter in the polymer particles I by not less than 5000, and wherein the glass transition temperature and the weight-average molecular weight of an acetone soluble-matter are determined as described in the description.