A communication apparatus including a metallic shelf having a pair of side plates, a back wiring board mounted in the shelf on the back side thereof and having a plurality of first connectors and a solid ground pattern, and upper and lower guide plates mounted in the shelf, each guide plate having a plurality of guide rails and a plurality of vent holes. A first shield board having numerous openings is mounted on the upper guide plate, and a second shield board having numerous openings is mounted on the lower guide plate. A plurality of plug-in units are mounted in the shelf so as to be inserted along the guide rails of the upper and lower guide plates.