A technique capable of preventing the loss of packet data for any appropriate one of controllers (100A to 100C) connected to the same network is provided. An FA system includes a plurality of controllers (100A to 100C). Each of the controllers (100A to 100C) includes: a buffer (150); a communication module (152) for performing packet communication with one or more other controllers; a packet monitor module (154) for buffering packet data generated in its own controller and packet data received by its own controller in the buffer (150); and a stop module (156) for stopping, in response to a predetermined stop condition (108) being satisfied, a buffering function of the packet monitor module (154) for a controller specified from the plurality of controllers (100A to 100C).
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