To provide a confluence improvement supporter capable of realizing a stable improvement in a confluence, in which an environmental and economical reduced.

A function communicating data between the confluence improvement supporter and a waterwork monitor 120 monitoring waterworks is mounted previously, waterwork data 2 such as the discharge of drainage, a demand curve, a water-distribution area (the place of coordinates and an area) or the like are procured by a communication from the waterwork monitor 120. The waterwork data 2 are converted into usable data (the demand curve at every divided area) for a sewage, the quantity of sewage, the quantity of rainwater, a sewage-quantity ratio, turbidity or the like is predicted by using the data and measured data such as the measured value of a rainwater meter, sewage- facility data, and water and sewage-work conversion data, and the result of the prediction is indicated to an operator.