The disclosure provides an antenna device and mobile terminal including such an antenna device. The antenna device includes a coil including a conductor wound around a plate-shaped magnetic core. A flat conductor is positioned adjacent to the coil, and the coil is positioned such that it is closer than the flat conductor to an antenna of a communication partner positioned near the antenna device. The coil conductor includes a first conductor portion adjacent to a first main surface of the magnetic core and a second conductor portion adjacent to a second main surface thereof. The magnetic core and the coil conductor form an antenna coil. A circuit substrate includes a ground electrode formation area and a ground electrode non-formation area. The antenna coil is mounted on the ground electrode non-formation area of the circuit substrate with the first main surface of the magnetic core facing the circuit substrate.