PROBLEM TO BE SOLVED: To provide method and system for electrolytic of a solid polymer which require less energy, which do not require maintaining high temperature, which can convert carbon dioxide as a profitable hydrocarbon compound, which control a creation amount of the hydrocarbon compound and a ratio for every kind, which improve use efficiency of created substance, and which facilitate equipment for separation and collection.SOLUTION: Carbon dioxide is supplied to a cathode 111 side of an electrolytic part 110 having a membrane electrode joint body 113, and water or steam is supplied to an anode 112 side. Applied voltage on the electrolytic part 110 is controlled for changing an amount of hydrocarbon compound created in unit time and a ratio for every kind.
