TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Arrangement: The portion which generates gas (b) is provided on the back surface through an insulation portion. Preferred Component: The hydrogen-producing apparatus further has conductive portion (c1), an electrode (e1), a conductive portion (10) which contacts electrode (e1) and portion which generates gas (b), an electrode (e2) provided between the back surface and portion which generates gas (a), two or more photoelectric conversion layers comprising p-type semiconductor layer, i-type semiconductor layer and n-type semiconductor layer, a top plate which opposes a substrate (1) provided on the portion which generates gas (a) and portion which generates gas (b), a space provided between portion which generates gas (a) and portion which generates gas (b), and a partition (13) for space between portion which generates gas (a) and top plate, and space between portion which generates gas (b) and top plate. The conductive portion is provided in the contact hole which penetrates the photoelectric conversion portion. The hydrogen-producing apparatus has one or more contact holes, and the total of cross-sectional area of each contact hole is 0.1-10% of area of light-receiving surface. Preferred Composition: The hydrogen-producing portion and oxygen generation portion comprise reactive catalyst which generates oxygen from electrolyte solution and which generates hydrogen from electrolyte solution. At least one of the catalyst of hydrogen-producing portion and oxygen generation portion is supported by a porous conductor. The partition comprises ion exchanger. Preferred Properties: The photoelectric conversion portion provided on the substrate has translucency. The photoelectric conversion layers have different band gaps. At least one of catalyst surface area of hydrogen-producing portion and oxygen generation portion is more than the area of the light-receiving surface.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Composition: The catalyst in the hydrogen-producing portion comprises platinum, iridium, ruthenium, palladium, rhodium, gold, iron, nickel and/or selenium. The catalyst in the oxygen generation portion comprises manganese, calcium, zinc, cobalt and/or iridium.