A foreign object detector, comprising: an oscillator circuit having a coil and a first (Cx) and second resonant capacitor (Cy), the oscillator circuit 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 configured to detect a variation of the AC component and a variation of the DC component in the voltage output from the oscillator circuit when a foreign object approaches the coil, wherein one electrode of the first resonant capacitor (Cx) is connected to one terminal of the coil and an output terminal of the oscillator circuit, one electrode of the second resonant capacitor (Cy) is connected to the other terminal of the coil, the other electrode of the first resonant capacitor (Cx) is grounded, and the other electrode of the second resonant capacitor (Cy) is grounded; characterized in that the first (Cx) and the second resonant capacitors (Cy) have a different capacitance from each other, and the electric circuit includes a rectifier circuit configured to rectify the voltage output from the output terminal of the oscillator circuit and to output the rectified voltage, and the rectifier circuit includes a first rectifier element for rectifying a voltage of the positive cycle, a first capacitor for reducing the DC component, and a second rectifier element for rectifying a voltage of the negative cycle which is smaller than zero due to reduction of the DC component. an oscillator circuit having a coil and a first (Cx) and second resonant capacitor (Cy), the oscillator circuit 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 configured to detect a variation of the AC component and a variation of the DC component in the voltage output from the oscillator circuit when a foreign object approaches the coil, wherein one electrode of the first resonant capacitor (Cx) is connected to one terminal of the coil and an output terminal of the oscillator circuit, one electrode of the second resonant capacitor (Cy) is connected to the other terminal of the coil, the other electrode of the first resonant capacitor (Cx) is grounded, and the other electrode of the second resonant capacitor (Cy) is grounded; characterized in that the first (Cx) and the second resonant capacitors (Cy) have a different capacitance from each other, and the electric circuit includes a rectifier circuit configured to rectify the voltage output from the output terminal of the oscillator circuit and to output the rectified voltage, and the rectifier circuit includes a first rectifier element for rectifying a voltage of the positive cycle, a first capacitor for reducing the DC component, and a second rectifier element for rectifying a voltage of the negative cycle which is smaller than zero due to reduction of the DC component. one electrode of the first resonant capacitor (Cx) is connected to one terminal of the coil and an output terminal of the oscillator circuit, one electrode of the second resonant capacitor (Cy) is connected to the other terminal of the coil, the other electrode of the first resonant capacitor (Cx) is grounded, and the other electrode of the second resonant capacitor (Cy) is grounded; characterized in that the first (Cx) and the second resonant capacitors (Cy) have a different capacitance from each other, and the electric circuit includes a rectifier circuit configured to rectify the voltage output from the output terminal of the oscillator circuit and to output the rectified voltage, and the rectifier circuit includes a first rectifier element for rectifying a voltage of the positive cycle, a first capacitor for reducing the DC component, and a second rectifier element for rectifying a voltage of the negative cycle which is smaller than zero due to reduction of the DC component. a first rectifier element for rectifying a voltage of the positive cycle, a first capacitor for reducing the DC component, and a second rectifier element for rectifying a voltage of the negative cycle which is smaller than zero due to reduction of the DC component.