To provide a DPF regeneration processing device for a vehicle, capable of improving the effective operability of an engine by shortening the automatic regeneration time of a DPF in the vehicle mounted with a diesel engine.

An exhaust gas after-treatment device for a diesel engine includes a DOC outlet exhaust gas temperature sensor for detecting a DOC outlet exhaust gas temperature; and a controller wherein either of the DOC outlet exhaust gas temperature detected with the DOC outlet exhaust gas temperature sensor and a detected value or a calculated value of an accumulated amount of PM is input and engine rotation speed at an idle operation when the accumulated amount of the PM is a certain threshold or below and the DOC outlet exhaust gas temperature is a fixed value or above after entering into an automatic regeneration process is retained at idling rotation speed which does not perform idle-up control and EGR passages of the engine are all closed.