An antenna device includes a feeding coil antenna and a booster coil antenna electromagnetically coupled to the feeding coil antenna. The feeding coil antenna includes a plurality of coil portions including at least one magnetic body and each including a coil conductor wound around the at least one magnetic body. The plurality of coil portions are connected to one another in an in-phase mode, and are arranged near one another such that winding axes of the coil conductors are oriented approximately in the same direction and at least portions of respective openings of the coil conductors face one another.