A water/oil repellent layer-provided substrate including a substrate, an undercoat layer formed on a surface of the substrate, and a water/oil repellent layer formed on a surface of the undercoat layer in this order. The water/oil repellent layer contains a condensate of a fluorinated compound having a reactive silyl group, the undercoat layer contains an oxide containing silicon and contains no alkali metal nor aluminum, and the substrate includes silica glass containing an alkali metal and aluminum.