In view of a communication system including communication apparatuses transmitting data and a distribution apparatus receiving data from each communication apparatus and distributing, it is provided with the distribution apparatus, the communication system and the communication method that implement reducing amounts of storage means utilized for temporally storing data received by the distribution apparatus from each communication apparatus.While the distribution apparatuses respectively include databases the databases are partitioned into common areas for storing data commonly shared with the distribution apparatuses and synchronized with each other, and non-common areas for storing data basically not transmitted between the ECUs connected to different communication lines. When receiving data from the ECU 4a, the distribution apparatus determines whether the received data should be stored on the common area or on the non-common area.