An antenna device includes two conductor surfaces facing each other and spaced apart from each other, connecting conductors that connect the two conductor surfaces at at least two positions, and an antenna coil located in proximity to one of the connecting conductors. The connecting conductors and the two conductor surfaces define a closed loop containing a surface of a space. In a plan view of the surface of the space defined by the closed loop, the antenna coil is located at a position where the antenna coil does not overlap the surface of the space and at a position where electromagnetic induction by the antenna coil causes an induced current to flow through the connecting conductor.