To accurately identify the starting timing of PM combustion by monitoring the oxygen concentration at a DPF exit side. To prevent the DPF breakage and melting loss due to continuing of post-injection even when the regeneration starts.

The particulate filter regenerating device regenerates a particulate filter 11 collecting the particulate contained in the exhaust gas of an engine 1 by post-injection. This device is comprised of an oxygen concentration detecting sensor 12 set at the exit side of the particulate filter 11, and a post- injection controller 20 stopping the post-injection when the oxygen concentration input from the oxygen concentration detecting sensor 12 is less than and equal to the setting.