A method for producing an oxynitride film includes: (A) supplying a first precursor containing a network former into a reactor in which a substrate is placed; (B) supplying at least one of an oxygen gas and an ozone gas into the reactor; (C) supplying a second precursor containing at least one of an alkali metal element and an alkaline-earth metal element into the reactor; (D) supplying at least one of a nitrogen gas and an ammonia gas into the reactor; and (E) supplying a purge gas into the reactor.