an antifouling resin (A) obtained by reacting in the presence of water a base resin including, in one molecule, a carboxyl group and a group having a polyalkylene glycol structure of formula (1) (CmH2mO)nR1???(1) wherein R1 is hydrogen, or a straight-chain, branched or cyclic alkyl group or aralkyl group having 1 to 20 carbon atoms, m is an integer of 1 to 4, and n is an integer of 1 to 100, with