An electrode active material has, as a main component, a mixture of an organic compound containing a rubeanic acid and oxamide. The rubeanic acid is represented by the following general formula: In the formula, n indicates an integer between 1 and 20, and R1-R4 indicate hydrogen atoms, halogen atoms, or a prescribed substituent group such as a hydroxide group, a 1-3C alkyl group, an amino group, a phenyl group, a cyclohexyl group, or a sulfo group.