Provided are a resin additive composition which is excellent in fluidity and can impart excellent physical properties to a thermoplastic resin, a thermoplastic resin composition, and a molded article thereof.
A resin additive composition is composed of a phosphoric acid ester compound (A) represented by the following general formula (1): (in the formula (1), R1 to R4 each independently represent a hydrogen atom or a linear or branched alkyl group having 1 to 9 carbon atoms, and R5 represents an alkylidene group having 1 to 4 carbon atoms) and a fatty acid sodium salt (B) represented by the following general formula (2): (in the formula (2), R6 represents a group introduced From an aliphatic organic acid having 7 to 30 carbon atoms), and the mass ratio of (B)/(A) is 0.55 to 2.0.