To prevent the clogging of a filtering means over a long period by supplying an acid to the filtering means when the device is suspended and sealing the device.

This device is provided with a line 10B for circulating a cationic coating material soln. in an electrodeposition tank 1 by pumps 15a and 15b and a line 20 for supplying a filtrate extracted from the coating material soln. with a filtering means 21 to washing chambers 5 and 6 and returning the filtrate recovered from the washing chambers 5 and 6 to the electrodeposition tank 1. Further, an acid supply means 40 is furnished to supply an acid dissolving the metallic compd. generated in the coating material soln. to the primary side of the filtering means 21. When the pumps 15a and 15b are stopped, the acid supply means 40 is driven, and an acid is sealed into the filtering means 21 until the pumps 15a and 15b are started. Consequently, since the inside of the filtering means 21 is replaced by the acid, the coating material component is never settled, a metallic compd. such as lead carbonate depositing on the filtering means is dissolved, and the clogging of the filtering means 21 is prevented over a long period.