A nuclide transmutation method comprising: an electrolytic solution supply step of supplying, via a supply mode that uses a flow of gas to force out a liquid, an electrolytic solution containing heavy water to a high deuterium concentration unit which forms an enclosed space that can be sealed by a structure comprising palladium or a palladium alloy, or a hydrogen-absorbing metal other than palladium or a hydrogen-absorbing alloy other than a palladium alloy, a high concentration formation step of electrolyzing the supplied electrolytic solution to generate deuterium, and producing a state of high deuterium concentration near the high deuterium concentration unit side surface of the structure, a low concentration formation step of placing a low deuterium concentration unit, which forms an enclosed space that can be sealed by the structure and is provided on an opposite side of the structure from the high deuterium concentration unit, in a state having a low deuterium concentration relative to that of the high deuterium concentration unit, and a nuclide transmutation step in which, as the deuterium penetrates through the structure from the high deuterium concentration unit toward the low deuterium concentration unit, a substance to undergo nuclide transmutation undergoes nuclide transmutation in the structure by reaction with the deuterium, characterized in that the method comprises: a gas discharge step of discharging gas from the high deuterium concentration unit generated during the high concentration formation step, and the electrolytic solution is supplied to the high deuterium concentration unit during the high concentration formation step. an electrolytic solution supply step of supplying, via a supply mode that uses a flow of gas to force out a liquid, an electrolytic solution containing heavy water to a high deuterium concentration unit which forms an enclosed space that can be sealed by a structure comprising palladium or a palladium alloy, or a hydrogen-absorbing metal other than palladium or a hydrogen-absorbing alloy other than a palladium alloy, a high concentration formation step of electrolyzing the supplied electrolytic solution to generate deuterium, and producing a state of high deuterium concentration near the high deuterium concentration unit side surface of the structure, a low concentration formation step of placing a low deuterium concentration unit, which forms an enclosed space that can be sealed by the structure and is provided on an opposite side of the structure from the high deuterium concentration unit, in a state having a low deuterium concentration relative to that of the high deuterium concentration unit, and a nuclide transmutation step in which, as the deuterium penetrates through the structure from the high deuterium concentration unit toward the low deuterium concentration unit, a substance to undergo nuclide transmutation undergoes nuclide transmutation in the structure by reaction with the deuterium, characterized in that the method comprises: a gas discharge step of discharging gas from the high deuterium concentration unit generated during the high concentration formation step, and the electrolytic solution is supplied to the high deuterium concentration unit during the high concentration formation step. a gas discharge step of discharging gas from the high deuterium concentration unit generated during the high concentration formation step, and the electrolytic solution is supplied to the high deuterium concentration unit during the high concentration formation step.