A signal line is drawn from a generally middle point of the antenna coil, and a capacitance-variable capacitors are connected at both sides of the antenna coil. This structure realizes a circuit in which a series resonance circuit composed of an antenna coil and a capacitor and an another series resonance circuit composed of an another antenna coil and an another capacitor are connected in parallel to each other across the generally middle point of the antenna coil to which the signal line is connected. Through the control of the resonance frequencies of the series resonance circuits, the parallel resonance frequency of the whole antenna is tuned to a desired frequency, and the resonance characteristic in which the impedance is matched to a specific value, e.g., 50 .OMEGA., can be achieved.