NOVELTY - The electrolytic vessel has side wall portion (17) that includes step-difference portion (45) to which space of inner surface of electrode (7) and inner surface of side wall portion is set larger than bottom side in the upper portion of electrolytic vessel. The step-difference portion is provided to convect bubble between liquid level (41) and step-difference portion by bubble buoyancy while accommodating and electrolyzing electrolyte solution and generating the bubble from inner surface of electrode.    USE - Electrolytic vessel for gas manufacturing apparatus for manufacturing gas such as hydrogen used as fuel for fuel battery and oxygen (all claimed).    ADVANTAGE - Since the step-difference portion is provided to convect bubble between liquid level and step-difference portion by bubble buoyancy while accommodating and electrolyzing electrolyte solution and generating the bubble from inner surface of electrode, the gas generated as bubble on the surface of the electrode for electrolysis is efficiently recovered even if the foam-separation apparatus is not provided and the size and cost of the gas manufacturing apparatus can be reduced. The bubble which adsorbs to the electrode surface for electrolysis can be decreased and the surface area of the electrode for electrolysis can be increased so that the gas can be generated effectively. The partition containing the ion exchanger can be provided so that the imbalance of the ion concentration which arises in electrolyte solution can be eliminated easily. Since electrodes for electrolysis are provided on the back surface of the photoelectric conversion unit, the light can be entered in the light-receiving surface of photoelectric conversion unit without electrolyte solution and the absorption of incident light and scattering of incident light by electrolyte solution can be prevented. The quantity of incident light can be increased to photoelectric conversion unit and the optical efficiency can be improved. The quantity of the bubble which adsorbs to the surface of the electrode for electrolysis increases so that the gas generation efficiency in the electrode surface for electrolysis can be reduced. Hence the decline in gas collection efficiency can be suppressed, the raise of the liquid level of electrolyte solution can be suppressed, and the decline in the gas generation efficiency in the electrode surface for electrolysis can be suppressed.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) gas manufacturing apparatus has photoelectric conversion unit that includes light-receiving surface and back surface. The electrode for electrolysis is parallelly provided on back surface so that electrolyte solution is electrolyzed using electromotive force which arises from photoelectric conversion unit light-receiving surface and gas is generated. The insulation portion is provided between electrode for other electrolysis, and back surface of photoelectric conversion unit. The electroconductive portion is provided in contact hole which penetrates photoelectric conversion unit to connect electrodes for electrolysis. The insulation portion is provided with opening on zones so that side surface of photoelectric conversion unit is covered. The photoelectric converting layer is composed of p-type-semiconductor layer, i-type semiconductor layer, and n-type-semiconductor layer. The photoelectric conversion unit is provided on translucency substrate (14). A hydrogen-producing unit is set to generate hydrogen from electrolyte solution among electrodes for electrolysis. An oxygen generation unit is set to generate oxygen from electrolyte solution. The porous conductor is provided to support catalyst from hydrogen-producing unit and oxygen generation unit. The hydrogen-producing catalyst is platinum, iridium, ruthenium, palladium, rhodium, gold, iron, nickel, and selenium. The oxygen generation catalyst is manganese, calcium, zinc, cobalt and iridium; and    (2) gas manufacturing method involves introducing electrolyte solution into gas manufacturing apparatus from lower portion so that the light-receiving surface of photoelectric conversion unit is inclined with respect to horizontal surface. The gases are generated from electrode for electrolysis by entering sunlight in the light-receiving surface of photoelectric conversion unit. The gases are discharge from upper portion of gas manufacturing apparatus.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view of the electrolytic vessel.    Electrode (7)    Substrate (14)    Side wall portion (17)    Liquid level (41)    Step-difference portion (45)