A device that wirelessly transfers power to an external device is provided. The device for wirelessly transferring power to an external device includes a resonant circuit including an adaptive circuit including at least one variable capacitor and a first inductor inductively coupled to the external device and configured to transfer the power to the external device using inductive coupling, and a first direct current (DC) power supply configured to apply a DC voltage to the adaptive circuit based on a control signal, wherein capacitance of the at least one variable capacitor is adjusted based on the DC voltage applied to the adaptive circuit.