A network system includes one or more terminals which transmit acquired data to a first network, a network interconnection device which is connected to the terminal via the first network and which receives the data from the terminal, and a management server which is connected to the network interconnection device via a second network and which receives the data from the network interconnection device; the terminal transmits the same data to the network interconnection device via the first network by a frequency corresponding to redundancy; the data contains the priority according to the contents of the data; and the network interconnection device acquires the communication quality of the second network and instructs the terminal to transmit the data according to redundancy determined based upon the acquired communication quality and the priority.