PURPOSE: To control the water level of a dam constantly and stably in response to the sudden change of the inflow of water to the dam, and to improve the accuracy of gate control.

CONSTITUTION: A plurality of gate operation plans are assumed (S1). Dam water levels at a time when the gate operation plans are carried out one by one are predicted (S2). Whether or not the dam water level by either gate operation plan is most favorable regarding the dam water levels predicted is evaluated by using a fuzzy inference (S3). Two top best evaluations are selected from each gate operation plan, a final gate manipulated variable is determined from the rate of the evaluation values and gate operation is executed (S4). Whether or not the dam water level is displaced from a predictor is detected (S5, S6). Gate control is completed when there is no displacement, and feedback control is conducted instantaneously when displacement is detected (S7).