An antenna device comprising an antenna element disposed on a mounting board separate from a main circuit board, a coupling means disposed on the mounting board such that it is electromagnetically coupled to the antenna element, and a frequency-adjusting means disposed on the mounting board such that it is connected to the coupling means, the antenna element comprising first and second strip-shaped antenna elements integrally connected for sharing a feeding point, the second antenna element being shorter than the first antenna element; the coupling means being formed on a dielectric chip attached to the mounting board, and having a coupling electrode electromagnetically coupled to part of the first antenna element. The frequency-adjusting means comprises a parallel resonance circuit comprising a variable capacitance circuit and a first inductance element, and a second inductance element series-connected to the parallel resonance circuit.