A resin composition having all of higher pigment colorability, low-temperature impact resistance, and flame retardance is provided. A graft copolymer is a polyorganosiloxane-containing graft copolymer formed by polymerizing one or more grafting vinyl monomers (b) in the presence of a rubber (A) containing polyorganosiloxane and a vinyl polymer, wherein the index of refraction of the rubber (A) is in the range of 1.47 to 1.56, and the volume-average particle size is in the range of 300 nm to 2000 nm. A resin composition contains the graft copolymer and a resin.