PURPOSE: To facilitate adding and changing modules and to reduce the manhour for maintenance, by selecting module corresponding to the combination between the kind of input telegrams and a center state of a matrix when a memory module receives the kind of input telegrams and the center state.

CONSTITUTION: A matrix table is generated preliminarily in a matrix 11 by center states 21 and the kind of telegram 22. In case of the input of an error response telegram, if the center state indicates the normal completion, the sequence is branched to a module A13 and a module B14, and the error response telegram is discriminated to terminate the processing. In respect to the control between modules, the matrix 11 is referred to on a basis of the kind of telegram 22 and center states 21; and if the kind of input telegrams indicates the request from a terminal and the center state 21 indicates the initial state, the sequence is branched to the module A13 and the module B14, and processings are performed independently of each other. Thus, addition and change of modules are facilitated to reduce the man-hour for maintenance.