PURPOSE: To permit real-time control flow rate of water by shortening the time of treatment by a method in which a fuzzy ratiocination is introduced to estimate the inflow rate to plan water level and effluent amount, and on the bases of the plan values, the opening degree of the reverse regulating gate is controlled.

CONSTITUTION: In a housing section 10 for data on inflow amount-predicting knowledge, membership functions, correcting coefficients, and fuzzy rules are housed, and in an inflow amount predicting section 11, an inflow amounts are predicted on the basis of these data. Also, in a water level and effluent planning section 13, the water level and effluent amount in dam are planned on the basis of the inflow amount predicted valued. Then, on the basis of the deviation-between the planned values and the water level in dam measured by the water level measuring section 15, the effluent plan value is corrected in an effluent target value arithmetic unit 17 to obtain an effluent target valued. In the opening degree target arithmetic unit, an opening degree target value for the reverse regulating gate 2 is calculated from the effluent target value, and in the correcting coefficient setter, the correcting coefficients are set and altered on the basis of the ratio between the water level measured value and the water level plan value.