Disclosed herein in a method of forming a metal oxide film, which can provide a high-quality metal oxide film while enhancing production efficiency. The method includes the steps of: turning a raw-material solution having a metallic element into a mist, to obtain a raw-material solution mist; turning a reaction aiding solution into a mist, to obtain an aiding-agent mist; feeding the raw-material solution mist and the aiding-agent mist into a mixing vessel, thereby mixing the raw-material solution mist and the aiding-agent mist, to obtain a mixed mist; and feeding the mixed mist onto a back surface of a substrate which is heated, to obtain a metal oxide film.