A scanning antenna provided with an array of a plurality of antenna units includes a TFT substrate, a slot substrate, and a liquid crystal layer disposed between the TFT substrate and the slot substrate. The slot substrate includes a second dielectric substrate, a slot electrode supported on a first main surface of the second dielectric substrate, and a first dielectric layer disposed between the second dielectric substrate and the slot electrode. The slot electrode has tensile stress. The first dielectric layer has compressive stress.