A vehicle resin for an antifouling coating composition, the vehicle resin being a copolymer comprising: a structural unit derived from a polymerizable monomer (a) having a silicon atom-containing group represented by the following formula: wherein in the formula, R 1, R 2, and R 3 each independently represent a hydrocarbon group having a carbon number of 1 to 6; and a structural unit derived from a polymerizable monomer (b) copolymerizable with the polymerizable monomer (a), wherein the polymerizable monomer (a) is a monomer represented by the following formula: wherein in the formula, R 1, R 2, and R 3 each independently represent a hydrocarbon group having a carbon number of 1 to 6, and R 4 represents a hydrogen atom or a methyl group, a content of the structural unit is greater than or equal to 50 mass% and less than or equal to 60 mass% in 100 mass% of the copolymer, a content of the structural unit is greater than or equal to 40 mass% and less than or equal to 50 mass% in 100 mass% of the copolymer, wherein the structural unit includes a structural unit derived from (meth)acrylic acid, and a content of the structural unit derived from (meth)acrylic acid is greater than or equal to 0.02 mass% and less than or equal to 8 mass% in 100 mass% of the copolymer, wherein the copolymer is characterized in that the polymerizable monomer (b) contains a monomer (b-2) containing an alkoxy group and/or an oxyalkylene chain in the ester moiety, and an acid value derived from free carboxy group is greater than or equal to 0.1 KOHmg/g and less than or equal to 60 KOHmg/g, wherein the acid value derived from free carboxy group in the copolymer is determined by neutralization titration using phenolphthalein as an indicator in accordance with JIS K 0070. a structural unit derived from a polymerizable monomer (a) having a silicon atom-containing group represented by the following formula: wherein in the formula, R 1, R 2, and R 3 each independently represent a hydrocarbon group having a carbon number of 1 to 6; and a structural unit derived from a polymerizable monomer (b) copolymerizable with the polymerizable monomer (a), wherein in the formula, R 1, R 2, and R 3 each independently represent a hydrocarbon group having a carbon number of 1 to 6; and a structural unit derived from a polymerizable monomer (b) copolymerizable with the polymerizable monomer (a), wherein the polymerizable monomer (a) is a monomer represented by the following formula: wherein in the formula, R 1, R 2, and R 3 each independently represent a hydrocarbon group having a carbon number of 1 to 6, and R 4 represents a hydrogen atom or a methyl group, a content of the structural unit is greater than or equal to 50 mass% and less than or equal to 60 mass% in 100 mass% of the copolymer, a content of the structural unit is greater than or equal to 40 mass% and less than or equal to 50 mass% in 100 mass% of the copolymer, wherein the structural unit includes a structural unit derived from (meth)acrylic acid, and a content of the structural unit derived from (meth)acrylic acid is greater than or equal to 0.02 mass% and less than or equal to 8 mass% in 100 mass% of the copolymer, wherein the copolymer is characterized in that the polymerizable monomer (b) contains a monomer (b-2) containing an alkoxy group and/or an oxyalkylene chain in the ester moiety, and an acid value derived from free carboxy group is greater than or equal to 0.1 KOHmg/g and less than or equal to 60 KOHmg/g, wherein the acid value derived from free carboxy group in the copolymer is determined by neutralization titration using phenolphthalein as an indicator in accordance with JIS K 0070.