A coil includes a resin substrate, a first coil structure formed on a first surface of the resin substrate, a second coil structure formed on a second surface of the resin substrate on the opposite side with respect to the first surface such that the second coil structure is formed at a position corresponding to the first coil structure, a third coil structure formed on the second surface such that the third coil structure is positioned adjacent to the second coil structure, and a fourth coil structure formed on the first surface such that the fourth coil structure is formed at a position corresponding to the third coil structure. The resin substrate is folded such that the second coil structure and the third coil structure oppose each other.