PURPOSE: To reduce the time necessary for opening and closing filter plates by providing freely slidably an intermediate head mounting a motor for driving a spline shaft which engages with a filter cloth driving shaft, to a central part of a side bar between loose heads for opening and closing the filter plates.

CONSTITUTION: Loose heads 3, 4 are moved to the center of a side bar 1 by the chains 8, 9 for driving the loose heads, and many filter plate groups are gathered closely to both sides of the intermediate head 12. Then, the loose head 3 and a cylinder head 6 are fixed to the side bar 1, and the loose head 4 is pushed toward the fixed loose head 3. Liquid to be filtered is fed to between the filter cloths 19 under this condition to perform filtration. Then, the loose heads 3, 4 are returned to the original positions by driving the chains 8, 9 in the reverse direction, and the driving motor 16 is driven to move the spline shaft 15; and the driving shaft 14 for filter cloth is turned in the same direction to cause running of the filter cloth 19. Thus, the cake sticking to the filter cloth 19 is stripped off.