The present invention relates to a water-soluble addition polymer which is produced from a carboxylated diol represented by the following general formula (I) and a polyisocyanate and has an acid value of 100 to 250, and an aqueous ink using this polymer as a dispersant for a disperse dye: wherein the residue A is an aromatic, alicyclic or aliphatic polybasic acid residue, and the residue B is a trivalent aliphatic alcohol residue.