An antenna device of the present disclosure includes: a dielectric layer; first and second conductor layers provided on both surfaces, respectively, of the dielectric layer; first and second antenna elements provided in the first conductor layer; a grounded conductor provided in the second conductor layer; and an EBG structure provided between the first and second antenna elements, wherein the EBG structure includes a first EBG portion provided in the first conductor layer, the first EBG portion including a plurality of first patch conductors electromagnetically coupled to the grounded conductor, and a second EBG portion provided in the second conductor layer, the second EBG portion including a plurality of second patch conductors electromagnetically coupled to the grounded conductor.