PURPOSE: To prevent cakes from producing cracks, by interposing a net to the middle of the thickness direction of the cake on a filter cloth in vacuum filtration.

CONSTITUTION: Firstly, a driving drum 2 is rotated to evacuate a vacuum box 12. Next, a slurry to be filtered is poured at a prescribed rate onto the holding side 11b of the horizontal surface 11a of a filter cloth 11. The poured slurry is sucked and dehydrated to form a cake layer 27 on the surface 11a. As the feeding rate of slurry is adjusted so that the thickness of the cake layer 27 is larger than a gap between the cloth 11 and a net 16, the net 16 enters in the layer 27 to move parallelly with the cloth 11. In this case, the net 16 acts on the layer 27 at the same role as that of a iron rod in a reinforced concrete, then the cake layer 27 is reinforced by the net 16, and the crack of cake is never produced even after the sucking dehydration is advanced.