PURPOSE: To prevent a trouble in a data collection device by making the content of a data subjected to packet processing and sent at a point of time identical to the content of a packet of other data exchange when one data switching is faulty and then restored.

CONSTITUTION: The 1st and 2nd data switching devices 10, 11 are provided as the data switching being a duplicated system so as to send a packet of the same content simultaneously. When the data switching devices, e.g., 11 is faulty and then restored, a packet reception transmission means 2 starts a timer 1 using a prescribed period being the cyclic reception of plural data and the processing of them into packets as a time for timeout, and receives the data from the data switching device 10 and sends them till the timer 1 expires. Thus, the content of the packet sent from the data switching device 11 is equal to the content of the packet sent from the data switching device 10. Thus, the occurrence of a trouble in a data collection device 12 is avoided.