PURPOSE: To solidify sludge with high efficiency by the procedure in which a sludge hardener is sent into stirring blades through introduction hole from the inside of rotary shaft by means of a pressure feeder and then jetted into sludge being stirred by the stirring blades from the nozzles on the side wall side of the stirring blade.

CONSTITUTION: The hollow rotary shaft 1 is given a rotation movement E and a vertical movement by an device (not illustrated), and the hollow shaft 1 is fitted with the T-shaped stirring blades 2 radially. The inside of the hollow shaft 1 consists of the horizontal portion A and the vertical portion B which are formed into a cavitied shape and connected to the hollow shaft A through the introduction hole 3. Also, the side walls C and D have the nozzles 4 and 4'. By a pressure feeder (not illustrated), a sludge hardener is sent into the stirring blades 2 through the introduction hole 3 from the inside of the shaft 1 and then jetted into sludge being stirred by the blade 2 from the nozzles 4 and 4'.