PURPOSE: To enable the perfect collection and the shaking-off of dust, by a method wherein a gas passage parallel with the primary side surface of a filter cloth and having said primary side surface of the filter cloth as a passage wall is formed in the primary side space of the filter cloth and a cleaning gas is blown from one side end of the gas passage while discharged to the primary side space of the filter cloth from the other end thereof.

CONSTITUTION: In a filtering process, a cleaning gas is flowed into a filter cloth cylinder 43 from the gap in a longitudinal direction between both ends of a guide place 47 and the filter cloth cylinder 43 and enters the inside of the filter cloth cylinder 43 through the entire surface thereof while exhausted from an exhaust port 49 as purified air. In a dust shaking-off process, an automatic valve 54 is fully opened and compressed air is supplied. Compressed air is injected downwards from plural blowing-in orifices 51 arranged to the outer periphery of the filter cloth cylinder 43 in a dispersed pattern and flowed into the gap between the filter cloth cylinder 43 and the guide plate 47. The procedure is continued until the automatic valve is fully closed and a filter cake adhered to the primary side of the filter cloth cylinder 43 is scattered.