A control system built around plural common objects is provided with greater flexibility and easy customizability, and a programming method for the control system is provided. An interface object (15) capable of two-way communications is created and used when first OCX (10), a common object, creates and controls second OCX (11). This interface object (15) is able to return events generated by second OCX (11) to first OCX (10), and first OCX (10) is able to completely control the operation of second OCX (11).