PURPOSE: To clean a discharge electrode at any time easily by firmly attaching a floating lever made of insulated material when a clutch is actuated and revolving a brush planted on the floating lever to brush the discharge electrode.

CONSTITUTION: A discharge electrode 16 is disposed obliquely close upper a drum 13 all over the whole of the axial direction of a drum 13. A floating lever 18 made of a U-shaped insured material with its central section parallel to a bus bar of the drum 13 is installed on an axis 25 of the drum 13 through a clutch 17, while a brush 19 with its motion locus intervening entirely with the discharge electrode 16 is planted on the upper side face of a central drum of the floating lever 18 in order to revolve the brush 19 around the axis 25 together with. As a result, cleaning of the discharge electrode can be carried out without damaging the discharge electrode at any time easily.