In an
exhaust gas treatment device in which a diesel oxidation catalyst and a DPF are provided in an
exhaust pipe of an
internal combustion engine, abnormal
combustion in the DPF, occurring when the
internal combustion engine varies from a
high load condition to a
low load condition, poses a problem. To solve this problem, in the present invention, a DPF abnormal
combustion causing operation is determined to have occurred when the
internal combustion engine shifts from a high rotation or
high load operation region α to a low rotation,
low load operation region β within a set time T1. When it is determined that a DPF abnormal
combustion causing operation has occurred, abnormal combustion of PM collected in the DPF is suppressed by fully opening an intake
throttle valve 44 in order to increase an
exhaust gas flow so that heat is removed by
sensible heat of the
exhaust gas, thereby cooling a DPF device 52, and continuing a late post-injection in order to reduce an
oxygen concentration of the DPF. As a result, an abnormal temperature increase in the DPF device 52 can be suppressed early.