PURPOSE: To allow a flame gas to reach a farther place so as to uniformly and sufficiently burn a soot layer of a filter cartridge by making flow resistance of the filter cartridge become greater in an area closer to a burner than in an area facing away from the burner.

CONSTITUTION: A soot filter has an inlet 2 and an outlet 3 in housing 1. The inlet 2 leads into an annulus 4, which surrounds a burner 5. The flame gases issuing from the burner 5 are deflected by a guide plate 6 and led into a filter bay 7, in which a considerable number of filter cartridges 8 extend parallel to one another. In this case, the filter cartridges 8 are divided into a first area 15 and a second area 16. Flow resistance of the filter cartridge 8 becomes greater in the area 15 located closer to the burner 5 than in the second area 16 facing away from the burner 5. Therefore, the flame gas can reach a further place, thus allowing uniform and sufficient burning of a soot layer in the filter cartridge 8.