Disclosed is a method of manufacturing a gas barrier film possessing a substrate in the form of a belt and provided thereon, a gas barrier layer containing silicon oxide, possessing a coating step in which a coating solution comprising a polysilazane compound is coated on the substrate to form a coating film, and a UV radiation exposure step in which the coating film is exposed to the vacuum UV radiation emitted from the plural light sources facing the substrate while moving the substrate on which the coating film is formed relatively to the plural light sources, the plural light sources each exhibiting even illuminance along a width direction of the substrate to form a gas barrier layer, and provided is a method of manufacturing a gas barrier film by which the gas barrier film suitable for production coupled with roll-to-roll system, exhibiting excellent gas barrier performance can be prepared.