To provide a supernatant water discharge device capable of preventing overflow from a settling pond due to severe rain. The supernatant water discharge device comprises: a submersible pump 10 provided in a first settling pond D; a floating member 30 that makes the submersible pump 10 float on a water surface; a distance sensor 41 that measures a distance to a sediment S; an anemometer 42; and a controller 50 that stops the submersible pump 10 if a measured value from the distance sensor 41 or the anemometer 42 reaches a threshold. By predicting severe rain, discharge of supernatant water W to a second settling pond P can be stopped. This can prevent overflow from the second settling pond P due to severe rain. If the sediment S gets close to the submersible pump 10 as a result of a drop in water level or increase in a deposition height, the submersible pump 10 can be stopped. This can prevent failure of the submersible pump 10 due to suction of a solid.