An optical method for modulo operations has been proposed. This method utilizes phase modulation of light wave. This method can be applied to modulo multiplication which is an important operation in an algorithm for prime factorization. Optical parallel processing based on the method is implemented with a Michelson interferometer. This report shows that this method is effective in prime factorization. Especially, we study on suitability between large scale data processing for the prime factorization and the proposed method.