To enable an electrostatic shield structure to display an electrostatic shield effect as much as possible, by a method wherein a means which decreases an object in impedance to grounding is provided to the electrostatic shield structure installed against a noise source.

Provided that noises are transmitted to a conductor 2 apart by a distance d1 from a noise source 1 that produces noises, an electrostatic shield structure 3 is installed at a position apart from the noise source 1 by a distance d2 (d2<d1). An impedance converter 4 as a means which decreases an object in impedance to grounding GND is connected to the electrostatic shield structure 3. By this setup, electrostatic capacitance between the noise source 1 and an equipment influenced by noises transmitted from the noise source 1 is reduced to nearly zero, a noise reduction mechanism of this constitution is capable of displaying an electrostatic shield effect as much as possible.