PURPOSE: To provide the water level control system which holds the water levels of downstream reservoirs, which branch from the same upstream reservoir and are connected in water processing facilities, etc., within a proper range only by measuring the water levels without directly measuring the passing water flow rates of the respective reservoirs.

CONSTITUTION: This system is provided with a control system 10 which starts the control operation of the water level control system at a certain-time period, and each downstream reservoir is provided with a level meter 4, a control valve 7, and a control valve controller 6 which inputs the measured value of the level meter each time a control system clock sends a reference period signal and calculates the manipulated variable of the control valve to control the valve, and further each upstream reservoir is provided with a water distribution pump 2 which sends out processed water, a water distribution flowmeter 8 which measures the amount of sent water, and a water distribution pump controller 9 which inputs the measured values of the level meters of the downstream reservoirs and the measured values of the water distribution flowmeters each time the control system clock sends the reference period signal, finds the flow rate of the water send by the water distribution pump by calculation, and controls the water discharge rate of the said water distribution pump so that the flow rate is obtained.