PURPOSE: To prevent exhaust gas particles from being discharged to the air, restrain excessive raise in exhaust gas pressure, and reduce reproducing energy.

CONSTITUTION: Three filters B1-B3 are disposed in parallel in an exhaust gas passage, and control valves C1-C3 which control the exhaust gas flow to the respective filters are installed. Besides, exhaust gas is made to flow into a filter in a low load range at the time of collecting and reproducing, exhaust gas is made to flow into two filters in the intermediate load range, and exhaust gas is made to flow into the three filters B1-B3 in the high load range Moreover, at the time of reproducing in the low load range, exhaust gas flow into the filter to be reproduced is stopped to make the exhaust gas flow into either of the remaining filters.