PURPOSE: To enable accurate and efficient inspection, by applying the output of a high frequency generator to an article to be inspected and judging the degree of discharge generated at the time of the application of said output on the basis of the magnitude of a discharge current.

CONSTITUTION: A secondary coil L2 boosts the output of a high frequency generator 1 and an electrode 2 is connected to a detection resistor 4 in series. A detection part 5 is constituted of a detection circuit 6 for detecting voltage generated in the resistor 4 when the output of the generator 1 is allowed to approach an article to be inspected through the electrode 2, an integrating circuit 7 for smoothing the detection output thereof and a differential amplifier 8 comparing the output of the circuit 7 with predetermined reference voltage. That is, when the voltage equal to or more than the predetermined reference voltage was generated in the resistor 4, output is obtained from the amplifier 8. If discharge equal to or more than a predetermined value is generated by an electric bulb, said discharge is displayed on a display means 9. By this method, inspection can be performed accurately and efficiently.