PURPOSE: To centrifugally separating substances having different specific gravities in a liquid by reduced power to be used without generating large noise, by rotating a porous screw in the liquid to be centrifugally separated stored in a horizontal container.

CONSTITUTION: A porous screw 4 is arranged in a horizontal funnel shaped container 1 through a bearing 2 and a liquid containing substances having different specific gravities is injected in said container 1 while the container is rotated at a high speed by a motor 5. When the porous screw 4 is rotated at a low speed, the liquid is quietly induced and rotated with the rotation of the screw 4 and subjected to gradual centrifugal separation. When the screw 4 is rotated at a high speed, positive and negative pressures are generaed before and behind the screw 4 but instantaneously neutralized by small holes and no harm caused by cavitation is generated and a stable high speed rotary stream is formed. By the centrifugal force due to this rotary stream, a substance having high specific gravity and a substance having low specific gravity are separated and the former is taken out from a circumferential outlet 7 while the latter from an outlet 8 on the basis of the difference in inertial force.