A coil for an antenna includes a ferrite core; and a winding conductor configured to have a conducting wire wound around the ferrite core as a core bar. The winding conductor includes an inner winding positioned inside when viewed from a plane perpendicular to the core bar, and an outer winding positioned outside of the inner winding. A length of the outer winding when viewed from a plane parallel to the core bar is different from a length of the inner winding.