PURPOSE: To restore an original image within a shorten time by executing operation by a mathematical argument based upon rise and full signal deterioration characteristics inherent in an application device itself and using each operated result successively to the succeeding operation.

CONSTITUTION: A signal level increasing rate of each fixed sampling time at the time of signal rise of a deteriorated signal from an original signal inherent in the application device itself and signal level reducing rate of each sampling time at the time of signal of the deteriorated signal are previously experimentally found out and stored in a video memory 4 or 7. An original image restoring part 5 executes operation so that the deteriorated signal is restored to the original signal based upon the signal level increasing rate or the signal level reducing rate corresponding to the number of times of sampling from the starting time of signal rise or signal fall in each sampling time in accordance with the lapse of time and uses each operated result to the succeeding sampling to execute the succeeding operation.