An antenna device (3a) comprises a substrate (11) and an antenna (21) provided on the substrate (11) and having an electrical length of ( lambda /2)xA (A is an integer). The antenna (21) includes a plate antenna (21b) disposed away from an edge (21d) by a distance equivalent to an electrical length of around lambda /4+( lambda /2)xB (B is an integer) and meandering line antennas (21a, 21c) connected to the plate antenna (21b).
