To permit the efficiency control of a furnace pressure with respect to the characteristics of an induced draft fan in an incinerating plant while contriving the energy saving required for the driving of the induced draft fan by employing inverter control (VVVF).

The furnace pressure in a waste incinerating plant is controlled by a method wherein waste gas is discharged employing an induced draft fan, controlled through inverter control based on the detection of the furnace pressure of an incinerator, through a bag filter type dust collector. The inverter control of the induced draft fan based on the detection of a furnace pressure is effected with a time constant of6 sec. or less, the primary delay of 130sec. or less in the increasing speed of 0-100% and 210sec. or less in the decreasing speed of 100-0%.