PURPOSE: To surely perform the dehydration of sludge, by contacting sludge with a compression belt at a loop angle smaller than the loop angle to the turning means of an endless screening belt.

CONSTITUTION: The titled apparatus constituted of a filter zone 10, a suction zone 12 and a pressure zone 14. The preparatorily dried sludge fed from the suction zone 12 by an endless screening belt 18 is compressed on the drive roller 20 of the pressure zone 14 by a compression belt 30 and separated from the above mentioned belt 18 as a paper like sludge cake. At this time, because the loop angle of the compression belt 30 around the drive roller 20 is smaller than that of the screening belt 18 around the same drive roller 20, the paper like band 74 of sludge can be simply separated from two belts. As a result, the dehydration of sludge can be surely performed.