PURPOSE: To clean a prefilter and electrode plates automatically and easily, by vertically moving a comb-shaped frame having a brush for cleaning a prefilter and flexible plates for cleaning electrode plates.

CONSTITUTION: A brush 31 for cleaning a prefilter is fixed to one side of a comb-shaped frame 30, and flexible plates 33 made of rubber or the like are fixed to protuberances 32 formed on the other side of the frame 30. The frame is fitted by bringing the brush 31 into contact with the prefilter, and the plates 33 into contact with electrode plates 4. A chain 36 is joinned with both ends of the frame 30, and the prefilter and the plates 4 can be easily cleaned by pulling the chain 36 with a motor to move the frame 30 up and down, rubbing the prefilter with the brush 31, and rubbing the plates 4 with the plates 33.