An object of the present invention is to provide a composition for forming an environment friendly antifouling coating film that can effectively exhibit an antifouling effect in seawater for a long period of time and furthermore exhibits a small temperature dependency of the coating film dissolving amount. The present invention provides an antifouling coating composition comprising: (A) a triorganosilyl ester-containing copolymer obtained by a mixture of (a) a triorganosilyl methacrylate monomer represented by a general formula (1) in which R1, R2, and R3 are equal or different each other, and each represent an alkyl group having 3 to 6 carbons and branched on α-position or a phenyl group, and (b) a methoxyalkyl methacrylate monomer represented by a general formula (2) in which R4 represents an alkylene group having 2 to 4 carbons, wherein a content ratio of the monomer (a) in the mixture is 45 to 65 weight %, and a total content of the monomer (a) and the monomer (b) in the mixture is 80 weight % or more, and a copper salt that is at least one member selected from the group consisting of rosin copper salts and copper salts of rosin derivatives.