A foreign object detecting device comprising: a first coil that includes a first wound wire having first and second terminals (T1, T2); a second coil that includes a second wound wire having third and fourth terminals (T3, T4) and is disposed adjacent to the first coil; a third coil that includes a third wound wire having fifth and sixth terminals (T5, T6) and is disposed adjacent to the second coil, the second coil being disposed between the first coil and the third coil, a winding direction of the third wound wire from the fifth terminal to the sixth terminal being the same as a winding direction of the first wound wire from the first terminal to the second terminal; and a foreign object detecting circuit; characterized in that the foreign object detecting circuit is operative to: output a first detecting signal having a first predetermined waveform to the first terminal of the first coil and output second detecting signal having a second predetermined waveform to the fifth terminal of the third coil to cause a combined magnetic field extending over the first and third coils (11a - 11c), a polarity of the second predetermined waveform being an inverted polarity of the first predetermined waveform; measure an amount of change of an impedance value with respect to one of the first and third coils (11a - 11c) corresponding to a change in the combined magnetic field which is caused by presence of a foreign object; and determine that the foreign object above the second coil is present if the amount of change exceeds a predetermined value, wherein potential of each of the second, fourth, and sixth terminals (T2, T4, T6) is at the same potential as a reference potential of the foreign object detecting circuit. a first coil that includes a first wound wire having first and second terminals (T1, T2); a second coil that includes a second wound wire having third and fourth terminals (T3, T4) and is disposed adjacent to the first coil; a third coil that includes a third wound wire having fifth and sixth terminals (T5, T6) and is disposed adjacent to the second coil, the second coil being disposed between the first coil and the third coil, a winding direction of the third wound wire from the fifth terminal to the sixth terminal being the same as a winding direction of the first wound wire from the first terminal to the second terminal; and a foreign object detecting circuit; characterized in that the foreign object detecting circuit is operative to: output a first detecting signal having a first predetermined waveform to the first terminal of the first coil and output second detecting signal having a second predetermined waveform to the fifth terminal of the third coil to cause a combined magnetic field extending over the first and third coils (11a - 11c), a polarity of the second predetermined waveform being an inverted polarity of the first predetermined waveform; measure an amount of change of an impedance value with respect to one of the first and third coils (11a - 11c) corresponding to a change in the combined magnetic field which is caused by presence of a foreign object; and determine that the foreign object above the second coil is present if the amount of change exceeds a predetermined value, wherein potential of each of the second, fourth, and sixth terminals (T2, T4, T6) is at the same potential as a reference potential of the foreign object detecting circuit. output a first detecting signal having a first predetermined waveform to the first terminal of the first coil and output second detecting signal having a second predetermined waveform to the fifth terminal of the third coil to cause a combined magnetic field extending over the first and third coils (11a - 11c), a polarity of the second predetermined waveform being an inverted polarity of the first predetermined waveform; measure an amount of change of an impedance value with respect to one of the first and third coils (11a - 11c) corresponding to a change in the combined magnetic field which is caused by presence of a foreign object; and determine that the foreign object above the second coil is present if the amount of change exceeds a predetermined value, wherein potential of each of the second, fourth, and sixth terminals (T2, T4, T6) is at the same potential as a reference potential of the foreign object detecting circuit.