A composition for forming a silica-based coating film includes a siloxane polymer and an alkali metal compound. The siloxane polymer is preferably a hydrolysis-condensation product of a silane compound having a hydrolyzable group. Sodium, lithium, potassium, rubidium, or cesium, or the like is used as the alkali metal of the alkali metal compound. Furthermore, the alkali metal compound is preferably a nitrate, sulfate, carbonate, oxide, chloride, bromide, fluoride, iodide, or hydroxide of the above alkali metal. This composition for forming a silica-based coating film may also include a pore-forming material. At least one material selected from amongst polyalkylene glycols and alkyl-terminated derivatives thereof is used as the pore-forming material.