To automatically move the level of a suction end and to surely remove and separate floating matter on the surface of liquid by vertically moving a cylindrical floating body floating out the surface of liquid with the vertical movement of the surface of the liquid in a bottomed cylindrical vessel associated with the operation of an impurity forced feeding pump.

When a device for removing suspended matter on liquid 1 is thrown into liquid in a tank K and is submerged, even an upper end 2A of a bottomed cylindrical vessel 2 is submerged in the liquid and the liquid gradually enters the inside of the bottomed cylindrical vessel 2 to float the cylindrical floating body 3 on the surface of the liquid through an air layer. Then, a notch part 9 of the cylindrical floating body 3 is projected form the surface of the liquid and an opening 8 of the cylindrical floating body 3 is abutted on a stopper 11 to stop the rising of the cylindrical floating body 3. In this state, an impurity forcibly feeding pump 15 is started to suck the liquid into an inner space S from the notch part 9. Then, the vertical movement of the cylindrical floating body 3 is repeated to suck a liquid layer part near the surface of the liquid into the inner space S together with suspended matter, which is removed from the surface of the liquid.