The present invention relates to a single-chamber or multichamber bag filter apparatus including horizontal and cross-sectionally flatly oval filter bags, each of which being provided with a rigid internal spacing element terminating at a distance before a perforated wall separating the dust gas side from the pure gas side and being loosely supported thereat. The filter bags including the spacing elements are releasably connected at their closed extremity to supports of an auxiliary wall springily mounted in front of the rear wall of the housing, and this auxiliary wall is coupled to an oscillation generator.