The present disclosure provides a method of shortening an aging period of a polymer electrolyte fuel cell immediately after production to increase shipping inspection speed and production speed of the polymer electrolyte fuel cell. The present disclosure relates to an aging method of a fuel cell which comprises a membrane electrode assembly comprising a fuel electrode, an electrolyte membrane, and an oxidant electrode, wherein the method comprises applying a potential cycle, wherein the lowest cell potential when a load is applied and OCV are alternately repeated between the fuel electrode and the oxidant electrode, and in the potential cycle, fuel gas is supplied to the fuel electrode, and oxidant gas and carbon monoxide gas are supplied to the oxidant electrode.