A cathode includes a lithium transition metal complex compound including lithium, one, or two or more transition metals, magnesium, and oxygen as constituent elements. In a standardized X-ray absorption spectrum of the lithium transition metal complex compound measured by an X-ray absorption spectroscopic method, a first absorption edge having absorption edge energy E1 in X-ray absorption intensity of about 0.5 exits in a range where X-ray energy is from about 1303 eV to about 1313 eV both inclusive, in a discharged state in which a discharge voltage is about 3.0 V, and a second absorption edge having absorption edge energy E2 in X-ray absorption intensity of about 0.5 exits, in a charged state in which a charge voltage V is from about 4.3 V to about 4.5 V both inclusive. The absorption edge energies E1 and E2 and the charge voltage V satisfy a relation of E2−E1≧(V−4.25)×4.