PURPOSE: To improve the discriminating accuracy of a combustion condition, by a method wherein, based on an image projected on a monitor a combustion condition in an incinerator is automatically discriminated, and this controls the combustion condition in the incinerator.

CONSTITUTION: An image, being monitored from the rear of an incinerator through a television set 2 for industrial use and a digitalizer 3, is converted into a digital signal to output it to a computer 4. In the image, a stoker surface, inclining downward in the direction of the rear, is represented. In said system, a burning-off point during a normal operation is located in a position A, but when a fire retardant substance is supplied, the burning-off point moves downward to a position B. The condition is discriminated by an image processor, and when moving downward from the position A by a specified distance, a feeder 5 and a stoker 6 are temporarily brought to a stop to measure the surface combustion of a solid waste substance. When the position of the burning-off point restores to the standard position A, the feeder 5 and the stoker 6 start to operate again.