To prevent the scattering of dust to the circumference at a time of the replacement of the filter cloth of a bag filter.

A moving truck 14 is provided on the lateral side of a position where a bag filter 12 is anchored and equipped with a lift jack 16 having a revolving device 15 attached thereto. A horizontal jack 19, a compressor 20 and a suction machine 21 are arranged to the upper end of the lift jack 16. The apparatus head 22 communicating with the compressor 20 and the suction machine 21 is supported on the leading end part of the horizontal jack 19. Filter cloths 4 are backward washed by the apparatus head 22 within the bag filter 12 and subsequently housed in a housing 23 to be again backward washed.