An antenna device includes an antenna element and a printed circuit board on which the antenna element is mounted. The antenna element includes a base, a radiation conductor formed on an upper surface of the substrate and one end of the radiation conductor being an open end, a plurality of terminal electrodes formed on a bottom surface of the substrate, and a loop conductor of a substantially U-shape. The loop conductor is arranged to face one of the terminal electrodes via a gap having a predetermined width. An antenna mounting region is provided on a upper surface of the printed circuit board to be adjacent to an edge of a long side of the printed circuit board. A feed line is led in the antenna mounting region along the edge. One and the other end of the loop conductor are connected to the feed line and a ground pattern, respectively.