An optical properties restoration apparatus improves reliability and longevity of optical properties of an optical system, lying upon a vacuum boundary, by preventing, suppressing, or improving degradation of optical properties. The apparatus includes creating the near vacuum zone to excite an oxidation reaction of carbon, generating a flow of an oxygen atom-containing gas such as water gas or oxide gas in the near vacuum zone, and supplying active energy in the near vacuum zone to cause a carbon oxidation reaction between the oxygen atom-containing gas and the carbon. The near vacuum zone faces the lighting surfaces of the optical system and a lower limit value for a partial pressure of the gases containing oxygen atoms that is supplied to the near vacuum zone is set to a level over a speed of the carbon buildup that deposits on the lighting surfaces of the optical system.