An antenna device, comprising: a first conductor layer; a second conductor layer that is located opposite to the first conductor layer; a first dielectric layer that is located between the first conductor layer and the second conductor layer; a third conductor layer that is located opposite to the second conductor layer; and a second dielectric layer that is located between the second conductor layer and the third conductor layer, wherein the first conductor layer includes: a feed element to which power is supplied; a first grounding element that is located next to the feed element in a first direction via a first gap and grounded; and a parasitic element that is 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 that is located opposite to the feed element and the parasitic element and insulated from the first conductor layer; and a second grounding element that is located opposite to the first grounding element and the parasitic element and next to the floating element in the first direction via a second gap, and grounded, and the third conductor layer includes a third grounding element that is located opposite to the floating element and the second grounding element and grounded, wherein the floating element and the second grounding element form a shape that is asymmetric with respect to the second gap. a first conductor layer; a second conductor layer that is located opposite to the first conductor layer; a first dielectric layer that is located between the first conductor layer and the second conductor layer; a third conductor layer that is located opposite to the second conductor layer; and a second dielectric layer that is located between the second conductor layer and the third conductor layer, wherein the first conductor layer includes: a feed element to which power is supplied; a first grounding element that is located next to the feed element in a first direction via a first gap and grounded; and a parasitic element that is located along the feed element and the first grounding element and insulated from the feed element and the first grounding element, a feed element to which power is supplied; a first grounding element that is located next to the feed element in a first direction via a first gap and grounded; and a parasitic element that is 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 that is located opposite to the feed element and the parasitic element and insulated from the first conductor layer; and a second grounding element that is located opposite to the first grounding element and the parasitic element and next to the floating element in the first direction via a second gap, and grounded, and a floating element that is located opposite to the feed element and the parasitic element and insulated from the first conductor layer; and a second grounding element that is located opposite to the first grounding element and the parasitic element and next to the floating element in the first direction via a second gap, and grounded, and the third conductor layer includes a third grounding element that is located opposite to the floating element and the second grounding element and grounded, wherein the floating element and the second grounding element form a shape that is asymmetric with respect to the second gap.