A control apparatus for controlling a machine, especially an injection molding machine, includes a bus board providing communication connections between different units, a wiring board, and a separate process module. The process module includes one or more process boards providing a base range of input/output (I/O) connections for the machines to be controlled. The process module can be directly connected to the bus board and the wiring board by means of a plug of second or third type, and thus produces a bridge, i.e. a connection, between the bus and wiring boards, thereby reducing wiring required between these boards At least one control module, which assumes the control tasks for the machine, can be plugged into the bus board by means of a plug contacts of first type.