A communication apparatus is provided which permits system configuration to be freely changed even after electronic circuit boards are mounted to a shelf. The apparatus is a combination of an open rack and a shelf mounted on the rack, office cables for interconnecting external electronic devices are guided toward the rear of the apparatus and connected directly to external connectors of the electronic circuit boards, and a back wiring board is arranged on the rear surface of the shelf and has sheet connectors to which power supply connectors of the electronic circuit boards are connected.