To omit the remake of a program even though a system using a single main controller is change to a system using plural distributed main controllers by operating a main module and an object module as the processes which are independent of each other.

In a main controller B, a single main process MP and the object processes OP1, OP2 and OP3 are operating independently of each other. The process MP includes a main module 1 and the object proxy modules 2, 3 and 4. The module 1 primarily performs the processing for an entire system, and modules 2 to 4 perform the processing for the monitor or control terminals via the interface devices D1, D2 and D3. Then the object modules 2', 3' and 4' manage the transmission of signals and the state of a central monitor controller.