PURPOSE: To improve the tuning efficiency of a membership function by applying the same membership function regardless of the scale of a dam, and to make transmission to a man such as the status decided in fazzy control are the reason of control easy to understand.

CONSTITUTION: A flow rate, a flow change rate, etc., are computed by a hydraulic compution means 3. A flow rate index as a value obtained by converting either of the flow rate or the flow change rate into the water level variation of a dam for a fixed time is computed by an index computation means 4. A fuzzy inference for controlling a gate is conducted by using flow rate index by a fuzzy inference means 7. A gate machine side disc 1 is controlled through a control arithmetic means 8 and a control output section 9 on the basis of an output from the fuzzy inference means 7.