A method for manufacturing a scanning antenna with a plurality of antenna units arrayed therein, the scanning antenna including a TFT substrate including a first dielectric substrate, a TFT, gate bus lines, source bus lines, and a plurality of patch electrodes, a slot substrate including a second dielectric substrate and a slot electrode including a plurality of slots disposed corresponding to the plurality of patch electrodes, a liquid crystal layer, and a reflective conductive plate, includes a step (a) of depositing a first conductive film containing copper on a first main surface of the second dielectric substrate, a step (b) of, after step (a), bringing the first conductive film into contact with an atmosphere to form an oxide film on a surface of the first conductive film, and a step (c) of, after step (b), depositing a second conductive film containing copper on the oxide film.