An antenna device (101) includes a first conductor plane (11) and a second conductor plane (12) that face each other. The first conductor plane (11) and the second conductor plane (12) are electrically continuous through a first connection conductor (21), a second connection conductor (22), and a chip capacitor (5). A power feed coil (30) is disposed between the first conductor plane (11) and the second conductor plane (12). The power feed coil (30) is composed of a magnetic core (30b) and a coil conductor (30a). The coil conductor (30a) forms a pattern such that the coil conductor (30a) winds around the magnetic core (30b). This power feed coil (30) is disposed at a position closer to the first connection conductor (21) and magnetically couples with the first connection conductor (21).