Provided are: a resin additive composition capable of imparting excellent antistatic effect in a small amount, and an antistatic thermoplastic resin composition. The resin additive composition contains two or more selected from aromatic metal phosphates (H) represented by the following Formula (3) or (4) in an amount of 0.001 to 50 parts by mass with respect to 100 parts by mass of a polymer compound (E). The polymer compound (E) has a structure in which a diol, an aliphatic dicarboxylic acid, an aromatic dicarboxylic acid, a compound (B) which contains at least one group represented by the following Formula (1) and has hydroxyl groups at both ends, and an epoxy compound (D) having two or more epoxy groups are bound via ester bonds: