An antenna device includes a power feed coil antenna connected to a power feed circuit, and a booster coil antenna including wound coil conductors and disposed so as to be electromagnetically coupled to the power feed coil antenna. The power feed coil antenna includes a first coil antenna and a second coil antenna each including a coil conductor, and the coil conductors of the first and second coil antennas are connected in phase with each other. The first coil antenna is disposed such that the winding axis of the coil conductor of the first coil antenna extends perpendicularly or substantially perpendicularly to the winding axis of the booster coil antenna, and such that at least a portion of the first coil antenna overlaps the coil conductor of the booster coil antenna as viewed in plan. The second coil antenna is disposed in the vicinity of the coil conductors such that the winding axis of the coil conductor of the second coil antenna extends in parallel with the winding axis of the booster coil antenna, and such that at least a portion of a coil opening of the second coil antenna does not overlap the coil conductors of the booster coil antenna as viewed in plan.