PURPOSE: To obtain the subject simple and polyfunctional apparatus for separating particles from a pulp flow and dividing the flow into fractions without needing the screening drum by providing specific second and third chambers for dividing the suspension flow after separation of undesired particles therefrom into the crude fraction and the fine fraction.

CONSTITUTION: The members 15, 24 are individually rotated with the common driving shaft 6 in front of the gaps 12, 22 to separate undesired particles from a suspension flow of cellulose fibers in the first chamber 9 and exclude them from the outlet 18 and the resultant suspension flow is divided into the crude fraction and the fine fraction from the outlets 27, 28 of the second chamber 10 and the third chamber 19. The radial extension of the annular gap 21 is made less than that of the annular gap 12, the projection element in the member 24 removes twigs, undissolved fiber bundles and the like, the space 26 between the projection elements is arranged at the right angle to the annular gap 21 to form the passage for a part of the suspension in the axial direction.