Abstract: In an apparatus for treating an exhaust gas from a diesel engine, including a filter unit in an exhaust gas passage for the diesel engine, the filter unit having a honeycomb structure wherein a plurality of cells are divided by cell walls having a filtration function and extend in the same direction as one another, predetermined cells being closed at one end, and the remaining cells being closed at the other end; the improvement comprises: back washing gas flow generating means for generating a gas flow at appropriate intervals so as to pass through the cell walls in the direction opposite to the flow of the exhaust gas flow, and a recollecting unit for particulates, which is provided in the exhaust gas passage at a position upstream to the filter unit.