A wireless power transmission device according to one embodiment of the present specification transmits wireless power to a wireless power reception device, and comprises: a power conversion circuit that transmits the wireless power to the wireless power reception device; and a communication/control circuit that communicates with the wireless power reception device and controls the wireless power, wherein the communication/control circuit transmits, to the wireless power reception device, a data packet comprising information on a number of slots and the length of the slots, for performing detection of foreign substances using the slots.