PURPOSE:To effectively analyze a factor of an accident, etc., by filing in order an operation state of a plant in the past, after an optional time, and displaying it on a CRT display device as necessary. CONSTITUTION:Whenever an abnormal state of a plant or a fault of an apparatus occurs, its state is displayed on a CRT display device 3 and also display data to which its time of occurrence has been added is filed in order to an auxiliary storage device 2. In this case, the file is used cyclically, and after the secured capacity has become full, the oldest editing data is removed and a newly generated data is adopted. In this way, the display data filed in the device 2 is suitably fetched in order as necessary, and it is displayed on the display device 3.
