In a metal oxide film formation method of the present invention, the following steps are performed. In a solution vessel, a raw-material solution including aluminum as a metallic element is turned into a mist so that a raw-material solution mist is obtained. In a solution vessel provided independently of the solution vessel, a reaction aiding solution including a reaction aiding agent for formation of aluminum oxide is turned into a mist so that an aiding-agent mist is obtained. Then, the raw-material solution mist and the aiding-agent mist are fed to a nozzle provided in a reactor vessel via paths. Thereafter, the raw-material solution mist and the aiding-agent mist are mixed in the nozzle so that a mixed mist is obtained. Then, the mixed mist is fed onto a back surface of a heated P-type silicon substrate.