NOVELTY - The carbon dioxide (CO2) in liquid at subcritical or supercritical state, and nonionic compound having CO2 affinity portion is added to mixture of aqueous solution containing metal salt and carbon dioxide, and electroplating is performed. CO2 affinity portion is homopolymer, copolymer or ternary copolymer, fluorine-containing alkyl group, fluorine-containing polyether group, and/or dialkyl siloxy group.    USE - For performing electroplating such as nickel plating on metal, and semiconductor wafer, electronic materials such as components used for fuel cells, injection-tip portions of inkjet printers, magnetic heads, components used for internal combustion engines, and components used for press pumps.    ADVANTAGE - The method efficiently and economically performs electroplating on metal, using plating liquid containing nonionic compound having favorable wetting property, emulsification ability, cleaning property and detachment defoaming ability of air bubble generated during electroplating.    DETAILED DESCRIPTION - The carbon dioxide (CO2) in liquid at subcritical or supercritical state, and nonionic compound having CO2 affinity portion is added to mixture of aqueous solution containing metal salt and carbon dioxide, and electroplating is performed. CO2 affinity portion is homopolymer, copolymer or ternary copolymer such as polyoxypropylene, polyoxybutylene and/or polyoxyethylene, fluorine-containing alkyl group with portions of hydrogen atom substituted by fluorine, fluorine-containing polyether group with portions of hydrogen atom substituted by fluorine, and/or dialkyl siloxy group. INDEPENDENT CLAIMS are included for the following:    (1) plating bath;    (2) additive for electroplating;    (3) pre-processing method of metal plating;    (4) post-processing method of metal plating; and    (5) metal-plated film.    DESCRIPTION OF DRAWING(S) - The figure shows the apparatus used for performing electroplating method.    carbon-dioxide cylinder (1)    thermostat (4)    anode (7a)    cathode (7b)    pressure regulator (10)