A wireless power transmitter includes a power conversion unit configured to transfer wireless power to a wireless power receiver by forming magnetic coupling with the wireless power receiver; and a communication/control unit configured to communicate with the wireless power receiver to control transmission of the wireless power and to perform transmission or reception of data, wherein the communication/control unit is configured to: receive, from the wireless power receiver after a configuration phase, a received power packet (RPP) which indicates a value of the wireless power received by the wireless power receiver; transmit, to the wireless power receiver, a bit pattern which requests communication initiated by the wireless power transmitter in response to the RPP when the communication/control unit has data to be sent to the wireless power receiver; and receive a packet for polling the data to be sent from the wireless power receiver in response to the bit pattern.