An antenna device includes a first planar conductor, a second planar conductor that opposes the first planar conductor in a parallel or substantially parallel arrangement, and a coil element with a winding axis that extends in a direction parallel or substantially parallel to the first planar conductor and the second planar conductor, and includes a first coil opening end and a second coil opening end that opposes the first coil opening end. The first planar conductor includes a conductor outer edge, and a conductor opening including a portion that is continuous with the conductor outer edge. At least a portion of the conductor opening is positioned inside a conductor overlapping region. The first coil opening end of the coil element does not overlap the second planar conductor, and the second coil opening end of the coil element overlaps the conductor opening and the second planar conductor.