A method for manufacturing an antenna device is provided. The manufacturing method includes forming an antenna circuit so that the resonance frequency of the antenna circuit will be lower than an oscillation frequency of the reader/ writer and affixing a magnetic sheet to an antenna coil via an adhesive. The antenna circuit includes the antenna coil that receives the magnetic field transmitted from the reader/ writer and a capacitor electrically connected to the antenna coil. The magnetic sheet is at a face-to-face position with respect to the antenna coil and is configured to change the inductance of the antenna coil. The adhesive is of a film thickness to change the inductance so that the resonance frequency of the resonance circuit will be coincident with the oscillation frequency depending on the spacing between the antenna coil and the magnetic sheet.