A foreign object detection device for a coil device including a second coil to transmit power to a first coil wirelessly or receive power from the first coil wirelessly including: a foreign object detection coil configured to be located between the first coil and the second coil; and a cover configured to cover an upper portion of the foreign object detection coil, wherein a top surface of the cover includes at least one inclined surface inclined relative to a coil plane of the second coil, and the inclined surface is inclined downward from a low sensitivity region where detection sensitivity of the foreign object detection coil is relatively lower to a high sensitivity region where the detection sensitivity of the foreign object detection coil is relatively higher.