A coil device includes a first coil pattern, a second coil pattern, an insulating layer, a magnetic covering element and a number of conductive pillars. The second coil pattern is disposed above the first coil pattern, and is spaced apart from the first coil pattern. The insulating layer covers the first coil pattern and the second coil pattern and defines an opening surrounded by the first coil pattern and the second coil pattern. The magnetic covering element covers the insulating layer and extends into the opening. The conductive pillars are disposed within the magnetic covering element and are exposed from a bottom side of the magnetic covering element. A portion of the conductive pillars are electrically connected to the first coil pattern, and another portion of the conductive pillars are connected to the second coil pattern. The coil device can be easily manufactured.