A foreign object detecting device includes first and second coils, the winding directions of which are the same, and a foreign object detecting circuit. The foreign object detecting circuit outputs a first detecting signal having a first predetermined waveform to a first terminal of the first coil and outputs a second detecting signal having a second predetermined waveform, which has the same polarity as the first predetermined waveform, to a third terminal of the second coil to cause magnetic fields generated from the first and second coils to repel each other. The foreign object detecting circuit measures an amount of change of the impedance value of the first or second coil which is caused by the presence of a foreign object. When the amount of change exceeds a predetermined value, the foreign object detecting circuit determines that there is a foreign object above the first or second coil.