An antifouling coating composition comprising a silicon atom-containing resin and a defoaming agent, wherein the defoaming agent includes a non-silicon-based defoaming agent or a fluorine-modified silicon-based defoaming agent, the silicon atom-containing resin includes a constituent unit derived from a monomer (a) having at least one kind of silicon atom-containing group selected from the group consisting of a group represented by a formula below, a group represented by a formula below, a group represented by a formula below, and a group represented by a formula below, the monomer (a) has a molecular weight of greater than or equal to 400 and less than or equal to 2500, and a content of the defoaming agent is greater than or equal to 0.7 parts by mass and less than or equal to 24 parts by mass with respect to 100 parts by mass of the silicon atom-containing resin: [in the formula, a and b each independently represent an integer of 2 to 5, m represents an integer of 0 to 50, and n represents an integer of 3 to 80; and R 1 to R 5 each independently represent an alkyl group, an alkoxy group, a phenyl group, a substituted phenyl group, a phenoxy group, or a substituted phenoxy group]; [in the formula, c and d each independently represent an integer of 2 to 5, and p represents an integer of 0 to 50; R 6, R 7, and R 8 each independently represent an alkyl group, R a, or R b; R a is (in the formula, x represents an integer of 0 to 20; and R 23 to R 27 are the same or different and each represent an alkyl group); and R b is (in the formula, y represents an integer of 1 to 20; and R 28 and R 29 are the same or different and each represent an alkyl group)]; [in the formula, e, f, g, and h each independently represent an integer of 2 to 5, q and s each independently represent an integer of 0 to 50, and r represents an integer of 3 to 80; and R 9 to R 12 each independently represent an alkyl group, an alkoxy group, a phenyl group, a substituted phenyl group, a phenoxy group, or a substituted phenoxy group]; and [in the formula, i, j, k, and 1 each independently represent an integer of 2 to 5, t and u each independently represent an integer of 0 to 50, and v and w each independently represent an integer of 0 to 20; and R 13 to R 22 are the same or different and each represent an alkyl group]. the defoaming agent includes a non-silicon-based defoaming agent or a fluorine-modified silicon-based defoaming agent, the silicon atom-containing resin includes a constituent unit derived from a monomer (a) having at least one kind of silicon atom-containing group selected from the group consisting of a group represented by a formula below, a group represented by a formula below, a group represented by a formula below, and a group represented by a formula below, the monomer (a) has a molecular weight of greater than or equal to 400 and less than or equal to 2500, and a content of the defoaming agent is greater than or equal to 0.7 parts by mass and less than or equal to 24 parts by mass with respect to 100 parts by mass of the silicon atom-containing resin: [in the formula, a and b each independently represent an integer of 2 to 5, m represents an integer of 0 to 50, and n represents an integer of 3 to 80; and R 1 to R 5 each independently represent an alkyl group, an alkoxy group, a phenyl group, a substituted phenyl group, a phenoxy group, or a substituted phenoxy group]; [in the formula, c and d each independently represent an integer of 2 to 5, and p represents an integer of 0 to 50; R 6, R 7, and R 8 each independently represent an alkyl group, R a, or R b; R a is (in the formula, x represents an integer of 0 to 20; and R 23 to R 27 are the same or different and each represent an alkyl group); and R b is (in the formula, y represents an integer of 1 to 20; and R 28 and R 29 are the same or different and each represent an alkyl group)]; [in the formula, e, f, g, and h each independently represent an integer of 2 to 5, q and s each independently represent an integer of 0 to 50, and r represents an integer of 3 to 80; and R 9 to R 12 each independently represent an alkyl group, an alkoxy group, a phenyl group, a substituted phenyl group, a phenoxy group, or a substituted phenoxy group]; and [in the formula, i, j, k, and 1 each independently represent an integer of 2 to 5, t and u each independently represent an integer of 0 to 50, and v and w each independently represent an integer of 0 to 20; and R 13 to R 22 are the same or different and each represent an alkyl group].