An antenna device includes a coil antenna including coil conductors that are wound around a winding axis and include a first coil end and a second coil end, a first planar conductor, a second planar conductor, and a third planar conductor. The first planar conductor includes a surface extending along the winding axis in proximity to the first coil end. The second planar conductor includes a surface extending along the winding axis is in proximity to the second coil end. The third planar conductor is in proximity to the first planar conductor and to the second planar conductor, with at least a portion of the third planar conductor being positioned between the first planar conductor and the second planar conductor in plan view.