A wireless power transfer method may include a selection phase of monitoring the placement and removal of an object for an interface surface of the power transmitter, a ping phase of receiving a response from a power receiver by performing digital ping using a first communication protocol, an identification/configuration phase of receiving a configuration packet including configuration information of the power receiver using the first communication protocol, wherein the configuration packet includes power class information of the power receiver and communication protocol information of the power receiver, a negotiation phase of selecting any one of the first communication protocol and a second communication protocol different from the first communication protocol based on the power class information and/or the communication protocol information using the first communication protocol, a calibration phase of improving the ability to detect a foreign object by controlling a specific parameter, and a power transfer phase of performing communication with the power receiver using the selected communication protocol and transferring power to the power receiver.