The scrubber according to one embodiment of the present application is for cleaning an exhaust gas to be recirculated to an engine, and comprises: a cleaning nozzle for injecting a cleaning liquid to the exhaust gas; a liquid storage tank for receiving the cleaning liquid injected from the cleaning nozzle and temporarily storing the cleaning liquid; a circulation pump for collecting the cleaning liquid stored in the liquid storage tank and supplying the cleaning liquid to the cleaning nozzle; a regulating valve for adjusting the discharge amount of the cleaning liquid discharged from the liquid storage tank so that the liquid level height of the cleaning liquid stored in the liquid storage tank becomes a reference height defined in advance; a level sensor that reacts to an object to be measured located above the reference height position of the liquid storage tank; a scum discharge port provided near the reference height position of the liquid storage tank; and a delivery nozzle for delivering, when the level sensor reacts to scum generated above the liquid level of the cleaning liquid, the scum toward the scum discharge port by injecting a liquid or a gas to the liquid level of the cleaning liquid stored in the liquid storage tank.