An antenna device is provided. The antenna device includes a first substrate, a first conductive layer, a first insulating structure, a second substrate, a second conductive layer and a liquid-crystal layer. The first conductive layer is disposed on the first substrate. The first insulating structure is disposed on the first conductive layer, and the first insulating structure includes a first region and a second region. The second substrate is disposed opposite to the first substrate. The second conductive layer is disposed on the second substrate. The liquid-crystal layer is disposed between the first conductive layer and the second conductive layer. The thickness of the first region is less than the thickness of the second region, and at least a portion of the first region is disposed in an overlapping region of the first conductive layer and the second conductive layer.