Abstract: A CRT operation apparatus comprising a CRT display for displaying an image of a plant, including the icons of the terminal devices incorporated in the plant, a low-rank controller for controlling the terminal units, and a high-rank controller for supplying various operation commands to the low-rank controller through a network. When an operator selects one of the icons displayed by touching the CRT display screen, thus selecting the corresponding terminal unit, the high-rank controller collects the first data item representing the condition of the selected terminal unit and the second data item representing the condition of that switch of a central control panel which has been operated to control the selected terminal unit, and supplies both data items in the form of an operable-signal or an abnormal-signal to the CRT display. The CRT display displays data showing whether or not the selected terminal unit can be operated further, in accordance with the signal.