The present disclosure provides a wireless power transfer method performed by a wireless power transmitter in a wireless power transmission system, and a device using same, the method comprising: establishing a power transfer contract with a wireless power receiver in a negotiation phase; and transferring the wireless power to the wireless power receiver on the basis of the power transfer contract in a power transfer phase, wherein the wireless power transmitter receives request information from the wireless power receiver in the negotiation phase, the request information includes information on a control error (CE) packet interval, and the wireless power transmitter transmits data to the wireless power receiver on the basis of the CE packet interval in the power transfer phase.