A foreign object detector includes: an oscillator circuit 100 having a coil 110 and resonant capacitors Cx, Cy, the oscillator circuit 100 being configured to output a voltage which includes an AC component and a DC component, the AC component having a positive cycle and a negative cycle; and an electric circuit for sensing a variation of the AC component and a variation of the DC component in the voltage output from the oscillator circuit 100 when a foreign object approaches the coil 110.
