An antenna device and an electronic device that includes the same are provided. The devices may each include a radiation conductor formed on a circuit board constituted by multiple layers, the radiation conductor being constituted by an electrically conductive pattern formed on at least one of the multiple layers constituting the circuit board or by a combination of electrically conductive patterns formed on the multiple layers, a ground conductor disposed on the circuit board to supply reference potential for the radiation conductor, a feeding line disposed on the circuit board to supply power to the radiation conductor, and a dummy conductor disposed on the circuit board, and the dummy conductor may be mounted to make contact with, or to be adjacent to, at least one of the radiation conductor, the ground conductor, and the feeding line.