A power transmitter includes a signal processor that externally obtains a reception power state signal depending on variation of a distance between transmission and reception coil units, a modulation controller configured to a modulation frequency for selecting a frequency band having maximum power transmission performance, based on the reception power state signal, a power signal generator that generates a power signal, and a modulator that modulates the power signal in response to the modulation frequency, the reception coil unit being configured to transmit the modulated signal. A power receiver includes a reception coil unit that receives a power signal, a power generator that generates power by receiving the power signal from the reception coil unit, and a signal generator that generates a reception power state signal depending on the generated power level and transmits the latter signal to a transmission coil unit corresponding to the reception coil unit.