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, the foreign object detection device comprising: a foreign object detection coil configured to be located between the first coil and the second coil; and the foreign object detection coil includes a detection loop that is a conductive wire of a loop shape, and characterized by: 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 (110a, 110b) inclined relative to a coil plane of the second coil, the inclined surface (110a, 110b) is inclined downward from a low sensitivity region (R LS1. R LS2) where detection sensitivity of the foreign object detection coil is relatively lower to a high sensitivity region (R HS) where the detection sensitivity of the foreign object detection coil is relatively higher, and the low sensitivity region (R LS1. R LS2) overlaps the conductive wire when viewed from a direction of a center axis of the detection loop and the high sensitivity region (R HS) overlaps an inner portion surrounded by the detection loop when viewed from the direction of the center axis of the detection loop. a foreign object detection coil configured to be located between the first coil and the second coil; and the foreign object detection coil includes a detection loop that is a conductive wire of a loop shape, and characterized by: 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 (110a, 110b) inclined relative to a coil plane of the second coil, the inclined surface (110a, 110b) is inclined downward from a low sensitivity region (R LS1. R LS2) where detection sensitivity of the foreign object detection coil is relatively lower to a high sensitivity region (R HS) where the detection sensitivity of the foreign object detection coil is relatively higher, and the low sensitivity region (R LS1. R LS2) overlaps the conductive wire when viewed from a direction of a center axis of the detection loop and the high sensitivity region (R HS) overlaps an inner portion surrounded by the detection loop when viewed from the direction of the center axis of the detection loop. 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 (110a, 110b) inclined relative to a coil plane of the second coil, the inclined surface (110a, 110b) is inclined downward from a low sensitivity region (R LS1. R LS2) where detection sensitivity of the foreign object detection coil is relatively lower to a high sensitivity region (R HS) where the detection sensitivity of the foreign object detection coil is relatively higher, and the low sensitivity region (R LS1. R LS2) overlaps the conductive wire when viewed from a direction of a center axis of the detection loop and the high sensitivity region (R HS) overlaps an inner portion surrounded by the detection loop when viewed from the direction of the center axis of the detection loop.