A scanning antenna includes a transmission and/or reception region including a plurality of antenna units and a non-transmission and/or reception region other than the transmission and/or reception region. The scanning antenna includes a TFT substrate, a slot substrate, a liquid crystal layer provided between the TFT substrate and the slot substrate, a seal portion provided in the non-transmission and/or reception region and surrounding the liquid crystal layer, a reflective conductive plate disposed opposing a second main surface of a second dielectric substrate with a dielectric layer interposed between the reflective conductive plate and the second main surface, a first spacer structure defining a first gap between a first dielectric substrate and the second dielectric substrate in the transmission and/or reception region, and a second spacer structure defining a second gap between the first dielectric substrate and the second dielectric substrate in the non-transmission and/or reception region, the second gap being wider than the first gap. The second spacer structure is disposed within the seal portion or within a region surrounded by the seal portion.