Provided is an antenna device with which the degradation of characteristics arising from the fact that the antenna has been miniaturized and made thinner is reduced and in which it is possible to increase the gain and to widen the coverage area by improving the characteristics of the internal antenna. The device is equipped with a circuit board, a wireless circuit component which is mounted on the substrate, an internal antenna which is connected to the wireless circuit component which is mounted on the substrate, a circuit-side ground pattern which is connected to the wireless circuit component which is mounted on the substrate, and a dedicated antenna ground paten which is connected to the internal antenna which is mounted on the circuit board.