A polymerizable composition for an optical material includes: an allyl carbonate compound (A) including two or more allyloxycarbonyl groups at a terminal which is represented by General Formula (1); and a radical polymerization initiator (B). The radical polymerization initiator (B) includes at least one kind of radical polymerization initiator (B1) which is a peroxyester-based radical polymerization initiator, and a radical polymerization initiator (B2). ##STR00001##

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): ##STR00001##
(in the formula (1), R.sup.1 to R.sup.4 each independently represent a hydrogen atom or a linear or branched alkyl group having 1 to 9 carbon atoms, and R.sup.5 represents an alkylidene group having 1 to 4 carbon atoms) and a fatty acid sodium salt (B) represented by the following general formula (2): ##STR00002##
(in the formula (2), R.sup.6 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.

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): ##STR00001##
(in the formula (1), R.sup.1 to R.sup.4 each independently represent a hydrogen atom or a linear or branched alkyl group having 1 to 9 carbon atoms, and R.sup.5 represents an alkylidene group having 1 to 4 carbon atoms) and a fatty acid sodium salt (B) represented by the following general formula (2): ##STR00002##
(in the formula (2), R.sup.6 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.