According to one embodiment, an electrode group is provided. The electrode group includes a positive electrode, a negative electrode, and a gel polymer layer interposed between the positive electrode and the negative electrode. At least a part of the negative electrode is opposed to the positive electrode. The gel polymer layer is formed of a gel electrolyte composed of a polymer material, an organic solvent and a lithium salt, and a sheet base member which supports the gel electrolyte, or the gel polymer layer is formed of only the gel electrolyte.