Abstract: One aspect of the present invention is an acidic gas separation device including: an electrolyte layer; a pair of electrodes provided with the electrolyte layer interposed between the pair of electrodes; and a voltage application unit that applies a voltage between the pair of electrodes, wherein the pair of electrodes are gas permeable electrodes, and the electrolyte layer contains: at least one selected from the group consisting of high molecular weight redox compounds having a radicalization rate of 90% or more, high molecular weight redox compounds having a quinone group in a molecule, and high molecular weight redox compounds having an imino group in a molecule; and a nonvolatile electrolytic solution.