A fiber channel switch (hereinafter, FC-SW) connected to a plurality of communications devices is provided with a buffer for temporarily storing data received from servers via a first communications port, a trace data storage memory for storing trace data, and a microprocessor (MP) for sending data accumulated in the buffer to a storage control system. The MP stores the information about the data about the received data into the trace data storage memory as trace data, issues a write command to the storage control system if it is detected that trace data sending condition is satisfied, and reads out the trace data stored in the trace data storage memory and sends it to the storage control system.