A wireless power transmitter apparatus is provided with: a power transmitter circuit having input terminals to which a DC power is inputted and output terminals from which the power transmitter circuit outputs the AC power and which supply the AC power to a power transmitting coil; a DC monitor circuit that monitors the DC power at the input terminals of the power transmitter circuit, and outputs a DC monitor signal indicating a change in a characteristic associated with the DC power; and a demodulator circuit that detects a load-modulated signal based on the DC monitor signal, demodulates the load-modulated signal, and outputs a first demodulated signal. The load-modulated signal is transmitted from the wireless power receiver apparatus to the wireless power transmitter apparatus by changing power consumption of the wireless power receiver apparatus.