An antenna device includes an antenna coil that receives a magnetic field transmitted from a reader/writer and a capacitor. The antenna device also includes a magnetic sheet formed at a face-to-face position with respect to the antenna coil and configured for changing the inductance of the antenna coil. The capacitor has a temperature characteristic in which the capacitance of the capacitor is changed with changes in temperature. The magnetic sheet is formed of a magnetic material having a temperature characteristic in which the inductance of the antenna coil is made to be changed with an opposite sign of change to that of the capacitance of the capacitor that is changed with changes in temperature in the working temperature range. In this manner, the resonance frequency of the antenna circuit in the working temperature range may be brought approximately into coincidence with the oscillation frequency of the reader/writer.