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 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, if the integrated time 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 of ash deposition in the DPF, if the short interval count reaches a predetermined necessary count for alarm, and wherein a short interval count having been already acquired is reset to 0, if the integrated time of the state of non-regenerative operation is a long interval not shorter than the predetermined decision time, before the short interval count 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 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, if the integrated time 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 of ash deposition in the DPF, if the short interval count reaches a predetermined necessary count for alarm, and wherein a short interval count having been already acquired is reset to 0, if the integrated time of the state of non-regenerative operation is a long interval not shorter than the predetermined decision time, before the short interval count reaches the predetermined necessary count for alarm. a timer; a counter; and an alarm device, wherein the timer measures integrated time 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, if the integrated time 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 of ash deposition in the DPF, if the short interval count reaches a predetermined necessary count for alarm, and