PURPOSE: To easily control a flood adjustment by detecting the water level, inflow quantity, and outflow quantity of a dam, and displaying the detection values, transition process, and target flow on a water level/flow graph.

CONSTITUTION: A water level/inflow quantity/outflow quantity detector 200 is provided, and the water level wl, inflow quantity wi, and outflow quantity wo of a dam are detected. A display means 100 displaying a graph 101 having the vertical axis for the water level (h) and the horizontal axis for the flow (f) is provided. The transition progress of the detection values and the target flow hfo are displayed on the graph 101. The situation is predicted and controlled based on the display. The flood adjustment situation can be properly grasped and easily controlled.