Abstract: A detection membrane (11) is joined to a first surface (10a) of an electrolyte membrane (10), and hydrogen gas is supplied to a second surface (10b) thereof. If the electrolyte membrane has a defect (10c), hydrogen gas leaks to the first surface, resulting in a change in electric resistance of the detection membrane near the defect. The defect is recognized by this change. FA hydrogen electrode (14) is joined to the second surface, and an electric circuit (17) is connected between the detection membrane and the hydrogen electrode. Hydrogen gas supplied to a space facing the hydrogen electrode is ionized at the hydrogen electrode, and hydrogen ions permeates through the electrolyte membrane and hydrogenates the detection membrane. Whether or not hydrogen ion conductivity is uniform is examined by measuring electric resistance of the detection membrane, which varies depending on the amount of hydrogen ions, for each of regions.