An electric energy generating apparatus configured to generate a desired electromotive force from hydrogen and oxygen is provided. The apparatus includes a hydrogen electrode film, an electrolyte film and an oxygen electrode film. The hydrogen electrode film, to which hydrogen is supplied, includes a catalyst layer containing a decomposing catalyst that decomposes hydrogen into protons and electrons. The electrolyte film includes a sheet having a plurality of voids. Oxygen is supplied to the oxygen electrode film. The voids in the electrolyte film are filled with proton-conducting material and/or the decomposing catalyst. This prevents the hydrogen from reaching the oxygen electrode film. When hydrogen is supplied to the hydrogen electrode film, the concentration of hydrogen of the oxygen electrode therefore decreased to such a value as required generating the desired electromotive force.