NOVELTY - Warm water is circulated to the electrode side and/or electrolytic membrane (14) of an electrode structure (20) of a polymer electrolyte fuel cell (10). Hydrogen is transferred to one electrode side by supplying hydrogen humidified at the other side, without supplying an oxidizing-agent gas at the side of one electrode in a state in which an electric potential is applied to the fuel cell (10). Electric-power generation aging is then carried out by setting a load current while supplying the oxidizing-agent gas and hydrogen to the fuel cell.    USE - Aging of polymer electrolyte fuel cell used in motor vehicles.    ADVANTAGE - The method enables efficient introduction of water into the electrolytic membrane, prevents consumption of hydrogen, and increases aging efficiency. Reduction of resistance overvoltage, concentration overvoltage, and active voltage is attained effectively. Aging time is shortened. The method is economical. Since impurities, such as residual solvent and adhesive material component, are removed, clean function is achieved.    DETAILED DESCRIPTION - Warm water is circulated to the electrode side and/or electrolytic membrane of an electrode structure consisting of a pair of electrodes arranged on both sides of a hydrocarbon-type electrolytic membrane, and a separator. Hydrogen pump aging is carried out by transferring hydrogen to one electrode side by supplying hydrogen humidified at the other side, without supplying an oxidizing-agent gas at the side of one electrode in a state in which an electric potential is applied to the fuel cell. Electric-power generation aging is then carried out by setting a load current while supplying the oxidizing-agent gas and hydrogen to the fuel cell. Warm water is pure water at 30-55 degrees C.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic explanatory view of the aging processing apparatus. (Drawing includes non-English language text)    Polymer electrolyte fuel cell (10)    Aging processing apparatus (12)    Electrolytic membrane (14)    Electrodes (16,18)    Electrode structure (20)