PURPOSE: To catch even fine particles and increase the quantity of caught particles, by using a purifier where an internal filtering type purifying means is arranged in the preceding stage in the direction of flow-in of air and a surface filtering type purifying means is arranged in the succeeding stage.

CONSTITUTION: Fine particles of a developing powder are carried to a filter 6 through an air duct by a discharge blower 7. Most of fine particles are caught on an internal filtering type filter 14 in the filter 6 by adhering. A small quantity of particles passing through the filter 14 are caught on a surface filtering type filter 15 arranged on the inside face of the filter 14. Therefore, the time required for causing clogging becomes about 6 times as long as that in case of the use of only the internal filtering filter. Thus, the running cost is reduced considerably.