To provide an inspection of pinholes or the like in an ion conductive electrolyte membrane.

A light-dimming thin film is jointed to one of the faces of the electrolyte membrane, and hydrogen gas is supplied from the other face of the electrolyte membrane. Since the hydrogen gas leaks toward one of the faces of the electrolyte membrane if there is a defective part such as a pinhole in the electrolyte film, by jointing the light-dimming thin film to that face, the light-dimming thin film is hydrogenated with leaked hydrogen gas at the defective part to have a reflective factor locally changed. That is, existence of possible defective parts can be quickly inspected, visually checking changes, if any, of local reflective factors of the light-dimming thin film.