In an electric potential difference forming step of a method of inspecting output of a fuel cell, a hydrogen gas as an anode gas is supplied to an anode, and an inert gas as a cathode gas is supplied to the cathode to generate an electric potential difference between the anode and the cathode. In a maintaining step, measurement current which is smaller than rated current of the fuel cell is applied to the anode and the cathode, and the voltage between the anode and the cathode is maintained at less than the reduction potential of the electrode catalyst. In a measurement step, in the state where the measurement current is applied to the anode and the cathode, and voltage between the anode and the cathode is maintained, the cathode gas is changed to a mixed gas, and then, output of the fuel cell is measured.