PURPOSE: To prevent the submergence of a sewage/rainwater sand sedimentation basin on the inflow side thereof and to efficiently perform control by operating a dust removing machine when the accumulation amount of the sludge flowing in the dust removing machine exceeds a prescribed amount or reaches a preset specific cycle time.

CONSTITUTION: The sewage/rainwater flowing in the sewage/rainwater sand sedimentation basin 2 in a sewage treatment plant is treated by a dust removing machine 3 and sent out by the discharge pump 5 arranged to a pump #4. At this time, in a dust removing machine control apparatus 8 equipped with a water level difference judging part 81, a water level judging part 82, a water level change rate judging part 83 and a specific cycle time judging part 84, the accumulation amount of the sludge flowing in the dust removing machine 3 is detected and an operation command is issued to the dust removing machine 3 on condition that it is judged that the inflow accumulation amount of sludge exceeds a prescribed amount or reaches a present specific cycle time large in time cycle. As a result, the submergence on the inflow side of the sewage/rainwater sand sedimentation basin can be prevented and useful and efficient control can be performed.