Electrode active material that is used together with an electrolyte solution having an electrolyte decomposition potential Ve is represented by the general expression LixFeMyO2 and is amorphous. In the expression, x and y are values which independently satisfy 1 < x = 2.5 and O < y = 3, respectively, and z = (x + (valence of Fe) + (valence of M) x y) / 2 to satisfy stoichiometry, and M representsone or two or more types of glass former element. The average electronegativity of M is less than (Ve + 6.74 / 5.41.