PURPOSE: To eliminate the need of an operator's judgement by collecting water level information such as a dam water level or the like to set constraint conditions on the water level, calculating the electric power quantity to create a virtual pattern, and correcting the virtual pattern at need to be made as the day's operation pattern.

CONSTITUTION: A generator is provided on a dam 1, and river system information such as a water level of each dam 1 or the like are transmitted from child machines 3 of a remote supervisory control unit to a parent machine 4. Subsequently, the information is input from the parent machine 4 to an operation pattern creating device 5 to create an operation pattern, In the device 5, the water level information is collected by a data collecting and setting means 51 to set the next day's operation pattern, and the quantity of electric power generated on the next day is calculated by a scheduled day's quantity calculating means 52. Then a virtual pattern is created by selecting the basis among a lot of model patterns by a virtual pattern creating means 53. The virtual pattern is corrected at need by a virtual pattern correcting means 54, and the corrected virtual pattern is registered as the next day's basic operation pattern by a pattern registering means 55.