A filter (41) traps particulate matter in the exhaust gas of a vehicle diesel engine (1). A vehicle speed sensor (51) detects a vehicle speed, and a controller (31) determines a vehicle running pattern from the vehicle speed. In the regeneration of the filter (41) to eliminate trapped particulate matter by burning, the controller (31) controls the exhaust gas temperature of the diesel engine (1) to a different target temperature according to the running pattern. As a result, there are less opportunities for regeneration of the filter (41) to be interrupted due to exhaust gas temperature drop, and regeneration of the filter (41) is ensured.