To obtain a water-cleaning device which can efficiently stir water in a water tank and simultaneously remove phosphates contained in the water without muddying the water in the water tank by disposing the water tank, a water receiver, a specific ion supplying means, a strainer, a water-returning way and a circulating means.

This water-cleaning device comprises a water tank for breeding organisms, a water receiver into which water in the water tank is transferred through a transfer route, an ion supply means 19 for supplying an ion for precipitating phosphates contained in the water to water in the water receiver, a strainer 4 disposed on the downstream side of the water receiver and used for straining the water, a water-returning way for returning the water passed through the strainer to the water tank, and a circulating means 6 for circulating the water in the water tank. Therein, it is preferable that the flow rate of the water circulated by the circulating means is larger than that of the water flowing in the water receiver.