A wireless power transmission method comprising: receiving, from a wireless power receiver (20, 700), a first foreign object detection status packet and a second foreign object detection status packet; wherein the first foreign object detection status packet includes a first reference value that is one of a reference quality factor and a reference peak frequency, and wherein a second foreign object detection status packet includes a second reference value, characterized in: transmitting, to the wireless power receiver (20, 700), a foreign object detection indicator indicating that a foreign object is present in a charging area of a wireless power transmitter (10, 600), wherein the first foreign object detection status packet includes mode information indicating that the first reference value is included in the first foreign object detection status packet, wherein the second foreign object detection status packet includes mode information indicating that the second reference value is included in the second foreign object detection status packet, wherein the second reference value is the other of the reference quality factor and the reference peak frequency, and wherein the foreign object detection indicator is generated based on the first foreign object detection status packet and then the second foreign object detection status packet. receiving, from a wireless power receiver (20, 700), a first foreign object detection status packet and a second foreign object detection status packet; wherein the first foreign object detection status packet includes a first reference value that is one of a reference quality factor and a reference peak frequency, and wherein a second foreign object detection status packet includes a second reference value, characterized in: transmitting, to the wireless power receiver (20, 700), a foreign object detection indicator indicating that a foreign object is present in a charging area of a wireless power transmitter (10, 600), wherein the first foreign object detection status packet includes mode information indicating that the first reference value is included in the first foreign object detection status packet, wherein the second foreign object detection status packet includes mode information indicating that the second reference value is included in the second foreign object detection status packet, wherein the second reference value is the other of the reference quality factor and the reference peak frequency, and wherein the foreign object detection indicator is generated based on the first foreign object detection status packet and then the second foreign object detection status packet. transmitting, to the wireless power receiver (20, 700), a foreign object detection indicator indicating that a foreign object is present in a charging area of a wireless power transmitter (10, 600), wherein the first foreign object detection status packet includes mode information indicating that the first reference value is included in the first foreign object detection status packet, wherein the second foreign object detection status packet includes mode information indicating that the second reference value is included in the second foreign object detection status packet, wherein the second reference value is the other of the reference quality factor and the reference peak frequency, and wherein the foreign object detection indicator is generated based on the first foreign object detection status packet and then the second foreign object detection status packet.