To obtain a network connection device and method with simple constitution and to attain a network including the device and method.

First and second networks consisting of plural nodes 106 to 133 having plural transmission lines and transmitting/receiving parts less than the number of transmission lines are mutually connected. Single or plural transmission lines in the 1st network are extracted and inserted into the 2nd network and the extracted transmission lines are prevented from being transmitted through the 1st network over a connection part. Single or plural transmission lines corresponding to the number of transmission lines extracted from the 1st network are extracted from the 2nd network and inserted into the 1st network and the extracted transmission lines are prevented from being transmitted through the 2nd network over the connection part. Consequently the inter- network connection system simply connects a specific channel from the 1st network to the 2nd network and from the 2nd network to the 1st network without generating the competition of channels.