PURPOSE: To enhance the dehydration rate of the title device as compared with the conventional unidirectional compression and suction by providing transfer rolls in multiple stages.

CONSTITUTION: The sludge supplied onto the horizontal part of a lower filter cloth 2 is successively passed through a gravity dehydration zone, a compression zone by a compression belt 4, and a compression zone by the transfer rolls 5 and 6, and dehydrated. In this process, the transfer roll devices are provided in plural stages in the final dehydration process. Consequently, the cake deposited on the transfer rolls 5 and 6 is scraped off by the scrapers 7 and 8 of the transfer roll device, dropped onto the lower filter cloth 2, and compressed. The operation is repeated. Accordingly, the water in the cake which could not be separated heretofore by the conventional unidirectional compression can now be separated.