Disclosed is a method of wirelessly transmitting, the method including: a selection phase for detecting each of power receivers and sending a digital ping to the each of power receivers; an introduction phase for receiving a request from the each of power receivers for a free slot; a configuration phase for providing a series of locked slots to the each of power receivers; a negotiation phase for receiving at least one negotiation data packet from the each of power receivers using the series of locked slots; a power transfer phase for transmitting power to the each of power receivers; and a renegotiation phase for returning to the negotiation phase, wherein the renegotiation phase is a phase for returning to the negotiation phase when a change of a charge status of at least one of the each of power receivers to which the power is transmitted is detected.