TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Composition: The amount of number-of-moles of carbon atom conversion of hydrocarbon-containing gas fed to anode side, mixed with waste gas from anode side is set, such that total of water vapor and carbon dioxide is more than equimolar ratio or double molar ratio.Preferred Method: The hydrocarbon-containing gas fed to anode side, and anode side waste gas are mixed, before touching the anode, and mixed gas is converted into mixed gas containing hydrogen and carbon monoxide by heat reaction. The anode side waste gas is mixed with oxygen or air, and obtained mixed gas is mixed with hydrocarbon-containing gas supplied to the anode side. The mixture is converted into a mixed gas containing hydrogen and carbon monoxide as a main component by partial-oxidation reaction heat of hydrocarbon-containing gas.Preferred Apparatus: A catalyst layer is arranged at the pipeline, which supplies mixed gas of water vapor and anode side waste gas to anode side of electrolytic cell.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The amount of number-of-moles of carbon atom conversion of hydrocarbon-containing gas fed to anode side, mixed with waste gas from anode side is set, such that total of water vapor and carbon dioxide is more than equimolar ratio or double molar ratio.Preferred Method: The hydrocarbon-containing gas fed to anode side, and anode side waste gas are mixed, before touching the anode, and mixed gas is converted into mixed gas containing hydrogen and carbon monoxide by heat reaction. The anode side waste gas is mixed with oxygen or air, and obtained mixed gas is mixed with hydrocarbon-containing gas supplied to the anode side. The mixture is converted into a mixed gas containing hydrogen and carbon monoxide as a main component by partial-oxidation reaction heat of hydrocarbon-containing gas.Preferred Apparatus: A catalyst layer is arranged at the pipeline, which supplies mixed gas of water vapor and anode side waste gas to anode side of electrolytic cell.