A communication system includes a bidirectional tree network having a base end and a plurality of terminating ends, a central apparatus connected to the base end, a plurality of terminating equipment connected respectively to the terminating ends, and a plurality of subscriber terminals accommodated respectively in the terminating equipment. Each of the terminating equipment has a multiplexer for multiplexing information transmitted from the subscriber terminal accommodated therein to the central equipment, and a signal selection device for discriminating and selectively receiving only information which is destined for the subscriber terminal accommodated in this terminating equipment from information transmitted from the central apparatus to all the subscriber terminals via the tree network. The central apparatus has an exchange equipment for discriminating destination of information transmitted from the subscriber terminals via the tree network, and a loop back device for scrambling the information transmitted from the subscriber terminals via the tree network so that the scrambled signal can be decoded only by a signal selection device corresponding to the discriminated destination and for sending back the scrambled information to the tree network.