An electricity storage device includes an electrode assembly configured such that first and second electrodes are layered. The electrode assembly includes two tab groups in each of which tabs of the first electrodes or the second electrodes having the same polarity are bundled. Each tab group and a conductive member are welded with each other by a welding portion. The welding portion has a mixed portion configured by mixing at least one of a metal that forms metal foils and a metal that forms the conductive member with a dissimilar metal that is different from the metal of the metal foils and has a higher electric resistivity than that of the metal of the metal foils.