Provided is a battery having a high charging/discharging capacity density as compared with a conventional one. The battery (1) is characterized by comprising a positive electrode (2), a negative electrode (3), and an electrolytic solution interposed between the positive electrode (2) and the negative electrode (3) and formed by dissolving an electrolytic solution in a solvent, wherein the positive electrode (2) includes rubeanic acid or a rubeanic acid derivative as an active material and the solvent includes an ionic liquid. In the battery (1), it is possible to neutralize, by anions present in the ions, positive charges generated when rubeanic acid or the rubeanic acid derivative is oxidized. Therefore, rubeanic acid or the rubeanic acid derivative can take three states from an oxidant to a reductant, so that a high charging/discharging capacity density can be obtained in comparison with a conventional one.