Provided is a surfactant which has a high surface tension reducing ability and a high solubility in a liquid medium, containing a fluorine-containing copolymer containing, as essential components, a monomer having a fluoroalkyl group having 1 to 7 carbon atoms, a hydrophilic monomer, and a monomer having an ion donor group. Further provided are a coating composition, an ink composition and a photographic emulsion composition, each comprising the surfactant.