DESCRIZIONE
[MEANS FOR SOLVING PROBLEMS] A novel cyclic carboxylic acid formed by the addition reaction of an unsaturated carboxylic acid with a conjugated diene compound; a metal salt of the acid; a compounding agent (A) for antifouling coating compositions which comprises at least one of the novel cyclic carboxylic acid, derivatives of the cyclic carboxylic acid (excluding the metal salts), metal salts of the cyclic carboxylic acid, and metal salts of the cyclic carboxylic acid derivatives; and an antifouling coating composition comprising the compounding agent (A) and a copolymer (B) for self-polishing type antifouling coating compositions. [EFFECTS] The composition can form an antifouling coating film which is reduced in environmental burden, evenly wears at a given rate over long, and can retain excellent antifouling performance over long. It is applicable also to ships and other objects for use in highly fouling waters.