An exhaust treatment device for a diesel engine, the device comprising: a DPF disposed on an exhaust path ; a differential pressure sensor that detects differential pressure between an exhaust inlet and an exhaust outlet of the DPF ; and a regeneration device , wherein the regeneration device performs DPF regenerating treatment that combusts PM deposited in the DPF , in response to that the differential pressure detected by the differential pressure sensor has reached a predetermined regeneration request value, the exhaust treatment device further comprising: a timer ; a counter ; and an alarm device , wherein the timer measures integrated time (IT) of a state of non-regenerative operation which ranges from an end of DPF regeneration to a next time point where the differential pressure reaches a regeneration request value, the counter acquires a short interval count (IC), if the integrated time (IT) is a short interval shorter than a predetermined decision time, the short interval count is incremented by 1 each consecutive time the integrated time is a short interval shorter than the predetermined decision time, and wherein the alarm device issues an alarm (S6) of ash deposition in the DPF, if the short interval count (IC) reaches a predetermined necessary count for alarm, and wherein a short interval count (IC) having been already acquired is reset to 0, if the integrated time (IT) of the state of non-regenerative operation is a long interval not shorter than the predetermined decision time, before the short interval count (IC) reaches the predetermined necessary count for alarm. a DPF disposed on an exhaust path ; a differential pressure sensor that detects differential pressure between an exhaust inlet and an exhaust outlet of the DPF ; and a regeneration device , wherein the regeneration device performs DPF regenerating treatment that combusts PM deposited in the DPF , in response to that the differential pressure detected by the differential pressure sensor has reached a predetermined regeneration request value, the exhaust treatment device further comprising: a timer ; a counter ; and an alarm device , wherein the timer measures integrated time (IT) of a state of non-regenerative operation which ranges from an end of DPF regeneration to a next time point where the differential pressure reaches a regeneration request value, the counter acquires a short interval count (IC), if the integrated time (IT) is a short interval shorter than a predetermined decision time, the short interval count is incremented by 1 each consecutive time the integrated time is a short interval shorter than the predetermined decision time, and wherein the alarm device issues an alarm (S6) of ash deposition in the DPF, if the short interval count (IC) reaches a predetermined necessary count for alarm, and wherein a short interval count (IC) having been already acquired is reset to 0, if the integrated time (IT) of the state of non-regenerative operation is a long interval not shorter than the predetermined decision time, before the short interval count (IC) reaches the predetermined necessary count for alarm. a timer ; a counter ; and an alarm device , wherein the timer measures integrated time (IT) of a state of non-regenerative operation which ranges from an end of DPF regeneration to a next time point where the differential pressure reaches a regeneration request value, the counter acquires a short interval count (IC), if the integrated time (IT) is a short interval shorter than a predetermined decision time, the short interval count is incremented by 1 each consecutive time the integrated time is a short interval shorter than the predetermined decision time, and wherein the alarm device issues an alarm (S6) of ash deposition in the DPF, if the short interval count (IC) reaches a predetermined necessary count for alarm, and <EOS>