An antenna device includes a prism-shaped or plate-shaped base member made of a dielectric or magnetic material, band-shaped first and second radiation conductors wound around the base member and connected to each other, and a third radiation conductor wound around the base member and connected to the second radiation conductor. The first and second radiation conductors include a plurality of divided portions, and the divided first radiation conductor portions are connected in series by first variable capacitance elements, the divided second radiation conductor portions are connected in series by second variable capacitance elements, and a node between the first and second radiation conductors is used as a feeding end.