Abstract: An optical apparatus includes a first electrode that can be kept in a transparent state in a visible light region, and a second electrode electrically separated from the first electrode. A space is provided between the first and second electrodes. A certain function is used to provide a driving potential to the first and second electrodes. An electrolyte is poured into the space between the electrodes. The electrolyte is composed of a solution prepared by dissolving a silver salt in at least one type of solvent selected from a group consisting of dimethylformamide, diethylformamide, N, N-dimethylacetamide, N-methylpropionamide, N-methylpyrrolidone, 2-ethoxyethanol, and 2-methoxyethanol. By use of this electrolyte, silver is precipitated and dissolved under driving control over the first and second electrodes. As a result, color-developing and color-fading are effected by precipitation and dissolution of silver, respectively.