An antenna device includes a substrate ground having a planar surface, a planar radiation element disposed in parallel and opposite to a planar portion of the substrate ground, a power feeding point connected to the planar radiation element, and a ground portion forming a stacked body in which, on a radiation surface side, ground patterns made of a conductive material are stacked from the radiation surface in a radiation direction perpendicular to the radiation surface. The ground pattern in each of layers of the stacked body is formed inwardly of a portion immediately overlying the ground pattern in another layer located on the radiation surface side, non-ground portions in which the conductive material is not disposed being formed in a portion immediately overlying the radiation surface, and the non-ground portions in the individual layers are formed to be gradually enlarged in the radiation direction.