A multistage relay communication system 100 includes a trunk network 1 and branch networks 2 (2a, 2b), each of which includes one or more communication apparatuses 4. The communication apparatus 4 can switch between a trunk mode to operate in the trunk network 1 and a branch mode to operate in the branch network 2. In the trunk network 1, the communication apparatus 4 carries out fixing of a communication path and redundancy of data based on a path table in order to achieve real-timeness and a data arrival rate. Meanwhile, in the branch network 2, when a communication failure occurs, the communication apparatus 4 autonomously searches for a communication path and constructs a path table, in order to at least secure a data arrival rate even if real-timeness is impaired within an allowable range.