To provide a method for treating steel-making sludge treated by a wet dust collector associated with a steel-making secondary refining process and stored together with circulating water in a storage tank under a condenser, without stopping secondary refining operation while keeping an operation cost extremely low.

The method for treating secondary refined sludge includes sequentially carrying out steps of operating secondary refining equipment to suck the secondary refined sludge treated by the wet dust collector attached to the secondary refining equipment and stored together with circulating water in the storage tank under the condenser, together with the circulating water into a recovery tank from the storage tank, and supplying a thickener with the circulating water and sludge sucked into the recovery tank to separate them into solids and circulating water.