A common mode filter includes a first iron core, a second iron core, a first coil, and a second coil. The first iron core includes two first electrode portions and two second electrode portions. The second iron core is disposed above the first iron core, and the first iron core and the second iron core are adhered to each other. All surfaces of the second iron core are coated with an insulating layer. The first coil is wound around the first iron core and the second iron core. The second coil is wound around the first iron core and the second iron core.