An object of the present invention is to allow an optical element to be obtained with good precision using a polymer film and a glass substrate as a reinforcer. The present invention is characterized by the fact that a polymer film is formed on a glass substrate which has been treated to prevent the glass substrate and polymer from separation. This allows an optical circuit pattern to be formed without producing separation between the glass substrate and polymer film when the film is formed. The dimensional precision of the configuration of the distributed index in the polymer film can be maintained generally to the same extent as the expansion and shrinkage of the glass substrate. In addition, a vessel obtained with a glass substrate as the bottom surface can be used as the casting vessel.