To regenerate a diesel particulate filter (10) which traps particulate matter contained in the exhaust gas of a diesel engine (20), a controller (16) raises the temperature of the exhaust gas through fuel injection control of a fuel injector (23), and thus burns the particulate matter trapped in the filter (10). The controller (16) controls the fuel injector (23) to raise the temperature of the exhaust gas to a higher temperature as the amount of particulate matter trapped in the filter (10) decreases, thereby-realizing effective regeneration while preventing the temperature of the filter (10) from becoming excessively high.