an address bus control system is provided of the type in which a controller including a central processing unit is connected through an address bus and a data bus to hardware modules which control equipment to be controlled . an address space defined by an address bus includes a discrimination space for discriminating the attribute of the hardware module and a function space for allocating and clearing an address space for a function interface of the hardware module . the attribute of a hardware module connected to a connector having a corresponding address is recognized using the discrimination space . the function interface of each hardware module is assigned a space within the function space in accordance with the contents of the discrimination space in concern , or the assigned space is canceled . an address of the function space can be allocated to only a necessary function interface , merely by connecting the hardware module to the connector , allowing to set up hardware modules equal to or larger than the total address space .