A solar-cell-integrated gas production device comprising: a photoelectric conversion part having a light acceptance surface and its back surface; a first electrolysis electrode provided on the back surface of the photoelectric conversion part so as to be capable of being immersed into an electrolytic solution; a second electrolysis electrode provided on the back surface of the photoelectric conversion part so as to be capable of being immersed into the electrolytic solution; and a changeover part, wherein the first electrolysis electrode and the second electrolysis electrode are provided to be capable of electrolyzing the electrolytic solution to generate a first gas and a second gas by utilizing an electromotive force generated by irradiating the photoelectric conversion part with light, when being irradiated with light, the photoelectric conversion part generates a potential difference between first and second regions on the back surface of the photoelectric part, the photoelectric conversion part is formed of at least one semiconductor material having an n-type semiconductor part and a p-type semiconductor part, wherein one of the first and second regions is a part of the n-type semiconductor part, while the other is a part of the p-type semiconductor part, wherein the first region is formed to be electrically connected to the first electrolysis electrode, the second region is formed to be electrically connected to the second electrolysis electrode, and the first region and the second region are electrically connected to the changeover part respectively, and the changeover part makes a changeover between a circuit that outputs the electromotive force, generated by irradiating the photoelectric conversion part with light, to a first external circuit, and a circuit that outputs the electromotive force, generated by irradiating the photoelectric conversion part with light, to the first electrolysis electrode and the second electrolysis electrode. a photoelectric conversion part having a light acceptance surface and its back surface; a first electrolysis electrode provided on the back surface of the photoelectric conversion part so as to be capable of being immersed into an electrolytic solution; a second electrolysis electrode provided on the back surface of the photoelectric conversion part so as to be capable of being immersed into the electrolytic solution; and a changeover part, wherein the first electrolysis electrode and the second electrolysis electrode are provided to be capable of electrolyzing the electrolytic solution to generate a first gas and a second gas by utilizing an electromotive force generated by irradiating the photoelectric conversion part with light, when being irradiated with light, the photoelectric conversion part generates a potential difference between first and second regions on the back surface of the photoelectric part, the photoelectric conversion part is formed of at least one semiconductor material having an n-type semiconductor part and a p-type semiconductor part, wherein one of the first and second regions is a part of the n-type semiconductor part, while the other is a part of the p-type semiconductor part, wherein the first region is formed to be electrically connected to the first electrolysis electrode, the second region is formed to be electrically connected to the second electrolysis electrode, and the first region and the second region are electrically connected to the changeover part respectively, and the changeover part makes a changeover between a circuit that outputs the electromotive force, generated by irradiating the photoelectric conversion part with light, to a first external circuit, and a circuit that outputs the electromotive force, generated by irradiating the photoelectric conversion part with light, to the first electrolysis electrode and the second electrolysis electrode.