An optical filter and a method of manufacturing the optical filter. Both principal planes of a substrate are polished by a polishing machine. After both principal planes of the substrate are polished, a first side film is deposited on one principal plane of the substrate by using a vacuum deposition method. While the film is deposited, a stress is applied to the one principal plane to deform the opposed end sides of one principal plane in the direction of the other principal plane. After a first film forming step, the deposited amount of a stress correction film on the other principal plane is set based on the deformed amount of the one principal plane by the formation of the first side film on the one principal plane, and the thickness of the stress correction film is set to a value equivalent to the thickness of a single layer film. In addition, by using the vapor deposition method, the stress correction film is deposited on the other principal plane to correct the deformation thereof by the formation of the first side film on the one principal plane for manufacturing the optical filter.