A network system includes at least one computer which includes a processor for processing data and attaching an associated contents code corresponding to the processed data and data group information indicative of a data group corresponding to the attributes of the processed data to ask a data transmission request and a transmission controller connected to the processor for controllably transmitting a frame including the transmission sub-network, the contents code and the processed data to the first sub-network according to the data group information of the processed data. A second computer connected judges whether or not the contents code of the frame received from the first sub-network conforms to one of a plurality of data reception enable/disable judgement conditions. A third computer judges whether or not the contents code of the frame received conforms to one of a plurality of data reception enable/disable judgement conditions, and storing the received frame having the contents code conforming to one of the plurality of data reception enable/disable judgement conditions. The second computer includes a filter in which the contents codes differently set for respective sub-networks are stored and which changes the contents code contained in the received frame to the contents code set for the receiving sub-network.