The present specification relates to a device and method for wirelessly transmitting power on the basis of the reestablishment of out-band communication. The present specification discloses a wireless power receiving device comprising a communication/control circuit configured to carry out the operations of: performing handover from in-band communication using operating frequencies to out-band communication using any frequencies except for the operating frequencies; transmitting power characteristic information to the wireless power transmitting device or receiving power characteristic information from the wireless power transmitting device through the out-band communication before entering a power transmission phase; and saving power state information determined during the power transmission phase. By defining an out-band communication reestablishment protocol for the wireless power transmitting device or wireless power receiving device, it is possible to improve the performance of wireless power transmission throughout-band communication reestablishment that is fast and efficient.