An antenna device includes a planar conductor, a coiled antenna element, and a feed coil. The feed coil includes a coil conductor wound around a magnetic core. The planar conductor includes a ground conductor provided with a printed wiring substrate. In a portion of a circumferential portion of the planar conductor, a coupling portion is provided and defined by an aperture and a slit. In a planar view of the antenna element, at least a portion of the coil aperture of the feed coil and a portion of the aperture overlap with each other. In addition, at least a portion of the coil aperture of the feed coil and a portion of the coil aperture of the antenna element overlap with each other.