To provide an optical density-changing element which has excellent properties that it can be brought into a colored state by applying only a low voltage, that it shows a rapid response speed and becomes completely colorless when restored to a bleached state from the colored state, and which can undergo a change in optical density in response to an applied voltage, the optical density-changing element includes, on each of an anode and a cathode, a material capable of at least one of donating and accepting an electron and, as a result of at least one of donating and accepting the electron, undergoing a change in absorption spectrum in a visible region and a material undergoing substantially no change in absorption spectrum in the visible region, with potentials of these materials satisfying a specific relation defined in the specification.