PURPOSE: To attain impartial processing and to allow a system to cope flexibly even with occurrence of a fault in the system where data packet processing is distributingly processed by plural packet processing units.

CONSTITUTION: Buffers 2 to 4 storing sequentially packet processing commands are provided corresponding to packet processing units 5 to 7. The packet processing command is shared to an idle buffer for the case. The packet processing units 5 to 7 receive the packet processing command from the corresponding buffers 2 to 4 to implement packet processing. Thus, loads are not concentrated in one packet processing unit but distributed. When a fault is detected in one of the packet processing units 5 to 7, a packet processing command in a corresponding buffer is distributed again to other idle buffer. Then data in the buffer corresponding to the processing unit having a fault are not lost but executed by other processing unit.