<p>Provided is a novel sludge flocculation method that can reduce the volumes pumped of the polymer flocculants necessary for the sludge flocculation, reduce the water content of the dewatered cake, and reduce waste matter volume. A sludge flocculation method is proposed, the method comprising: a first stirring process of pumping a first polymer flocculant solution into the sludge and mixing the sludge with the first polymer flocculant solution by high speed stirring at 1000 rpm or more to prepare a mixed sludge; and a second stirring process of pumping a second polymer flocculant solution into the mixed sludge and mixing the mixed sludge with the second polymer flocculant solution by stirring at 10 - 500 rpm to form a flocculated floc.</p>
