PURPOSE: To improve dust collecting efficiency remarkably by utilizing a filter itself as an electrode of an electric dust collecting machine.

CONSTITUTION: A positive DC high voltage is impressed to a forestage filter 9 sandwiched by metallic nets 7 from a high voltage block 12. A poststage filter 10 sandwiched by metallic nets 8 is provided in parallel to said filter 9 and is used as a dust collecting electrode. Dust 15 is ionized by the positive DC high voltage while the dust passes through the filter 9, and ionized finer dusts 16 which are not caught by the filter 9 and pass through the filter 9 are caught by the filter 10 at the succeeding stage effectively because the filter 10 functions also as a dust collecting electrode.