PURPOSE: To prevent a liquid-jetting pipe from being buried in waste washing liquid at the time of washing treatment by means of a simple construction, by supporting a liquid jetting pipe at its middle parts with the aids of liquid-jetting- pipe supporting members, and shifting the pipe from its horizontal posture to vertical one with the movement of a bed of liquid jetting pipe for performing the washing treatment.

CONSTITUTION: A moving bed 6 is disposed above a filter-plate arranging part so as to make the bed 6 freely movable in the opening direction of filter plates 2, and a liquid-jetting pipe feeding bed 7 is made freely movable in the horizontal direction parallel to the surface of the filter plate with respect to the bed 6. On the other hand, a pipe 5 is made freely turnable in the plane parallel to the surface of filter plate by holding a connecting end part of the pipe 5 at the side of a washing-liquid supplying pipe 8 by means of the bed 7. And the pipe 5 is supported in order at the middle parts of it by liquid-jetting pipe supporting members 9, 10 hanging down from respective parts of the bed 6, and then, the filter plates 2 and filter cloths are washed by shifting the pipe 5 from its horizontal posture to vertical one with the movement of the bed 7. In this case, the pipe 5 is released from the member 10 when its posture is vertical.