A wireless power receiver for transferring a power received from a wireless power transmitter to a load, the wireless power receiver including a receiving coil configured to receive an AC power from the wireless power transmitter, a rectifier configured to rectify the AC power into a DC power and a controller configured to monitor a DC voltage at an output of the rectifier, in which the wireless power receiver transceives information with the wireless power transmitter through an in-band communication, and the controller creates a control signal to adjust the AC power received from the wireless power transmitter and continuously is configured to charge the load when a charging state is changed.