A gas blocking layer forming apparatus comprises a vacuum chamber that provides a space where a chemical vapor deposition process and a sputtering process are performed; a holding unit that is provided at a lower side within the vacuum chamber and mounts thereon a target object on which an organic/inorganic mixed multilayer gas blocking layer is formed; a neutral particle generation unit that is provided at an upper side within the vacuum chamber and generates a neutral particle beam having a high-density flux with a current density of about 10 A/m2 or more; and common sputtering devices that are provided at both sides of the neutral particle generation unit, wherein each common sputtering device has a sputtering target of which a surface is inclined toward a surface of the target object.