A message communication method and system in which a message signal to be communicated includes a function code signal portion and a data signal portion, the former being an index to the content of the latter and forming the substantial part of the message signal, and in which such a message signal is communicated not only among equipment blocks connected with one and the same communication line but also among those connected with different communication lines coupled with each other through a common equipment block connected with both of the coupled communication lines. Function codes being indices to the contents to data required to be processed by equipment blocks connected with the coupled communication lines are respectively registered in different memories in the common equipment block and the function code signal portions of message signals received by the common equipment block are compared with the stored function codes in the common equipment block and if concurrence takes place transferrence of the message signals between the coupled communication lines is effected.