To provide an N:N communication system capable of performing the communication of N:N by using an existing 1:1 communication port.

In this communication system S for making plural devices 1-6 provided with an intrinsic ID number 9 mutually communicable by using the existing 1:1 communication port P, a signal line (w) from the communication port P of an analyzer 1 is connected to the communication ports P of the adjacent two analyzers 2 and 4 by dividing one to the input side of communication data Td and the other to an output side and a communication loop L for limiting the communication direction of data Dt to one is formed as the whole. Also, the respective devices 1-6 are identified by the ID number 9 and provided with a communication program 8 for making the data Dt transferable to each other.