PURPOSE: To aim at reducing necessary installations, by arranging a slurry stirring tank in addition to a plurality of slurry tanks which are commonly communicated thereto so that there is no need for installing a stirrer in each slurry tank, so the reduction of installation cost is attained.

CONSTITUTION: There are provided a plurality of slurry tanks 1 in a ship. Each slurry tank 1 is provided with a guide wall 1a inclined toward a discharge port 7 in the bottom of the tank 1 and a pipe line 9 connected to a common slurry stirring tank 4 through a pump 8. Further, a common pump 10 for sucking supernatant liquid in each tank 1 and leading the latter to the common slurry stirring tank 4, is arranged. Accordingly, slurry having a high concentration in each slurry tank 1 is led by the pump 8 into the slurry stirring tank 4 from the discharge port 7, while supernatant liquor is led by the pump 10 to the tank 4 so that the slurry is stirred to have a suitable concentration and then returned to each tank 1 through a pipe line 12.