Method and aparatus of transmitting communication power in wireless power transmit system

The charge power transmission method and device in a wireless power transmission system is disclosed. Whether the charge power transmission according to an embodiment may be made by determining whether to transmit a charging power to the wireless power receiving device, the wireless power transmission device based on the output information of the DC / DC converter of the wireless power receiving device. Wireless power transmission device may transmit the power to the wireless power receiving communication device if it determines that it does not send a charge power.