To obtain a noise reduction apparatus by which a noise generated inside an enclosure can be reduced by a method wherein the inside of the enclosure provided with a printed-wiring member is partitioned by a mesh-shaped conductive member covered with an insulator and the conductive member is connected electrically to the enclosure.

The whole of a copying machine is constituted of a frame body composed of a pillar-shaped metal frame 1, and a plastic enclosure 2 whose surface is treated so as to be conductive is installed at the outermost part of the metal frame 1. In addition, four conductor meshes 4(a) to 4(d) are installed so as to surround a printed-wiring board 3. The conductor meshes are attached in such a way that they can be connected electrically to the metal frame 1 by conductor-mesh mounting screws 5 at their peripheral parts. Thereby, an electromagnetic noise which is generated inside the enclosure can be reduced, and a temperature rise inside the enclosure can be suppressed.