A detection coil includes a first sub coil disposed on a first PCB, the first sub coil includes a first part, and a second part that is disposed under the first part and that includes: one end connected to one end of the first part and is wound in a direction opposite to a direction the first part is wound. The detection coil includes a second sub coil disposed on a second PCB and including a third part and a fourth part disposed under the third part. The fourth part includes one end connected to one end of the third part, and is wound in a direction opposite to a direction the third part is wound. The first and second parts have polygonal shapes symmetrical to each other. The third and fourth parts have polygonal shapes symmetrical to each other. The first and second sub coils are arranged to partially overlap each other.