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) cumulatively calculates
the time during which the temperature of the filter (10) exceeds a target
temperature as an effective regeneration time. By estimating the amount
of particulate matter remaining in the filter (10) on the basis of the
effective regeneration time, the controller (16) estimates the amount of
remaining particulate matter with a high degree of precision and without
consuming energy, whereupon regeneration of the filter (10) through fuel
injection control ends.