An antenna device includes: a first conductor layer; a second conductor layer located opposite to the first conductor layer; and a third conductor layer located opposite to the second conductor layer. The first conductor layer includes: a feed element; a first grounding element located next to the feed element in a first direction and grounded; and a parasitic element located along the feed element and the first grounding element and insulated from the feed element and the first grounding element. The second conductor layer includes: a floating element located opposite to the feed element and insulated from the first conductor layer; and a second grounding element located opposite to the first grounding element and next to the floating element and grounded. The third conductor layer includes a third grounding element grounded.