PURPOSE: To efficiently recover solid sludge, by throwing sludge in a tank having a net part and injecting high pressure water to said sludge to grid the same.

CONSTITUTION: After solid sludge was thrown in a sludge throw-in tank 15, high pressure water is injected from a high pressure water jet nozzle 20 to grind the solid sludge. High pressure water is prevented from scattering by a scattering preventing plate 18 and a support and scattering preventing plate 19 to prevent the contamination of the circumference. When the ground sludge is ground so as to have a size passing through the meshes of a net 17, said sludge is flowed out from the sludge throw-in tank 15 to be stored in a liquid collection tank 16 and dispersed and dissolved in a solvent. The formed dispersion or solution is sent to a dissolving and separation tank 3 where a solid component is removed and subsequently sent to a tank 9 having the solvent stored therein and water is separated while the sludge is recovered in the solvent.