This invention relates to an aqueous ink jet ink emulsion obtained by emulsion polymerization of (b) an ethylenic unsaturated bond-containing monomer under the presence of (a) a hydrophilic group-, hydrophobic group- and radical reactive group-containing reactive emulsifier, and there is provided an additive (polymer emulsion) having an effect of improving print quality (print density, abrasion resistance and glossiness) of printed matter by adding the emulsion to an aqueous ink.