A wireless power transmitter which performs communication with one or more wireless power receivers, includes a power converter including at least one coil configured to convert current into magnetic field, and a power transmission controller configured to communicate with a wireless power receiver based on a frame, wherein the frame includes a sync pattern and a plurality of slots which have different slot numbers respectively, wherein the sync pattern indicates a first slot as allocated to the wireless power receiver, wherein the power transmission controller receives a first packet from the wireless power receiver in the first slot having a first slot number, and receives a second packet from the wireless power receiver in a second slot having a second slot number, and wherein the second packet includes an information field indicating the first slot number.