A wireless power transmission method of a wireless power transmitter comprising: transmitting a first state information of the wireless power transmitter to a wireless power receiver; receiving a first state information of the wireless power receiver from the wireless power receiver; and transmitting a first power corresponding to the first state information of the wireless power receiver to the wireless power receiver; wherein the first state information of the wireless power transmitter comprises a first available power of the wireless power transmitter and a maximum power of the wireless power transmitter, wherein the first state information of the wireless power receiver comprises a first demanded power of the wireless power receiver, wherein the first demanded power of the wireless power receiver is determined by the wireless power receiver within the first available power of the wireless power transmitter, and wherein the first available power of the wireless power transmitter is a power value which can be supplied by the wireless power transmitter to the wireless power receiver, the wireless power transmission method being characterized by: detecting a state change of the wireless power transmitter, wherein the change of the state of the wireless power transmitter refers to information about the change of the amount of power to be supplied from the wireless power transmitter; transmitting a second state information of the wireless power transmitter to the wireless power receiver; receiving a second state information of the wireless power receiver from the wireless power receiver; and transmitting a second power corresponding to the second state information of the wireless power receiver to the wireless power receiver, wherein the second state information of the wireless power transmitter comprises a second available power of the wireless power transmitter, wherein the second state information of the wireless power receiver comprises a second demanded power of the wireless power receiver, and wherein the second demanded power of the wireless power receiver is determined by the wireless power receiver within the second available power of the wireless power transmitter. transmitting a first state information of the wireless power transmitter to a wireless power receiver; receiving a first state information of the wireless power receiver from the wireless power receiver; and transmitting a first power corresponding to the first state information of the wireless power receiver to the wireless power receiver; wherein the first state information of the wireless power transmitter comprises a first available power of the wireless power transmitter and a maximum power of the wireless power transmitter, wherein the first state information of the wireless power receiver comprises a first demanded power of the wireless power receiver, wherein the first demanded power of the wireless power receiver is determined by the wireless power receiver within the first available power of the wireless power transmitter, and wherein the first available power of the wireless power transmitter is a power value which can be supplied by the wireless power transmitter to the wireless power receiver, the wireless power transmission method being characterized by: detecting a state change of the wireless power transmitter, wherein the change of the state of the wireless power transmitter refers to information about the change of the amount of power to be supplied from the wireless power transmitter; transmitting a second state information of the wireless power transmitter to the wireless power receiver; receiving a second state information of the wireless power receiver from the wireless power receiver; and transmitting a second power corresponding to the second state information of the wireless power receiver to the wireless power receiver, wherein the second state information of the wireless power transmitter comprises a second available power of the wireless power transmitter, wherein the second state information of the wireless power receiver comprises a second demanded power of the wireless power receiver, and wherein the second demanded power of the wireless power receiver is determined by the wireless power receiver within the second available power of the wireless power transmitter. detecting a state change of the wireless power transmitter, wherein the change of the state of the wireless power transmitter refers to information about the change of the amount of power to be supplied from the wireless power transmitter; transmitting a second state information of the wireless power transmitter to the wireless power receiver; receiving a second state information of the wireless power receiver from the wireless power receiver; and transmitting a second power corresponding to the second state information of the wireless power receiver to the wireless power receiver, wherein the second state information of the wireless power transmitter comprises a second available power of the wireless power transmitter, wherein the second state information of the wireless power receiver comprises a second demanded power of the wireless power receiver, and wherein the second demanded power of the wireless power receiver is determined by the wireless power receiver within the second available power of the wireless power transmitter.