To provide a detecting device of a conductive foreign matter for a high voltage apparatus capable of surely detecting even a minute conductive foreign matter by achieving high detecting sensitivity, enhancing decision accuracy of the presence of the conductive foreign matter, and enhancing insulation reliability.

A DC power source 3 is connected to a high voltage conductor 1 housed in a metal tank 2 through pulse obstructing impedance 4. A pulse power source 5 is connected to the high voltage conductor 1 through a combined capacitor 6. The DC power source 3 applies DC bias voltage to the high voltage conductor 1, and pulse power source 5 superimposes pulse voltage on the DC bias voltage and applies it to the high voltage conductor 1. Then, polarity of the DC voltage and that of the pulse voltage are made opposite.