To provide a refractive index modifier, which can enhance a refractive index of a thermoplastic resin without deteriorating the transparency of the thermoplastic resin when mixed in the thermoplastic resin, and to provide a thermoplastic resin composition, in which the refractive index modifier is mixed, and a molded product of the resin composition.

A refractive index modifier comprises a dithiocarbonate compound represented by formula (I) as an ingredient. A (meth)acrylic resin composition or a polyester resin composition contains the refractive index modifier.