An antenna device includes a core, a bobbin member having a partition, and a coil provided around the bobbin member. The coil is configured with a tight winding portion and a loose winding portion. The tight winding portion is provided between one bobbin side and the partition. The loose winding portion is provided between the other bobbin side and the partition. The loose winding portion is configured with a first winding layer and a second winding layer. A wire winding direction of the first winding layer is opposite to a wire winding direction of the second winding layer so that the wire of the first winding layer and the wire of the second winding layer cross and overlap to each other along part of the bobbin member.