At least three resonance frequencies are obtained by two antenna elements. The antenna device includes antenna elements (11) and (12), a wireless section (20) for supplying power to each of the antenna elements (11) and (12), a PIN diode (16) for electrically connecting and disconnecting the antenna element (11) and the wireless section (20) with/from each other, the antenna elements (11) and (12) being provided so as to be capacitively coupled to each other during the electrical disconnection between the antenna element (11) and the wireless section (20) which electrical disconnection is made by the PIN diode (16).