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, a seal portion surrounding the liquid crystal layer, a wall structure (additional seal portion) disposed in a region surrounded by the seal portion in the non-transmission and/or reception region, a reflective conductive plate, a first spacer structure defining a first gap between a first dielectric substrate and a second dielectric substrate in the transmission and/or reception region, and a second spacer structure disposed in the wall structure and defining a second gap wider than the first gap. The wall structure includes a first main side face and a second main side face that intersect a surface of the first dielectric substrate, and at least one of the first main side face and the second main side face includes a plurality of recessed portions and/or a plurality of protruding portions when viewed from a normal direction of the first dielectric substrate.