PURPOSE: To eliminate even a noise having a narrow pulse width and high energy density by using a coil and a capacitor to a circuit connecting a resistor and a coil in parallel.

CONSTITUTION: The coil 3 and the capacitor 6 are connected respectively in series and parallel with the parallel circuit comprising the coil 4 and the resistor 5. In selecting values of each coil, the resistor and the capacitor so as to satisfy a prescribed relation, most of the current due to noise having a short pulse width flows to the resistor 5, is attenuated by the circuit constituted with the resistor 5 and the capacitor 6, and since almost no noise current flows to the coil 4, the attenuating oscillation is not produced. Since the amount of timewise change of the noise current flowing to the capacitor 6 is suppressed by the coil 3, the voltage drop caused by a residual inductance of a lead or the like of the capacitor 6 is decreased.