To provide an exhaust gas aftertreatment device of a diesel engine capable of increasing an exhaust gas temperature to normally operate a DOC and a DPF particularly at low load of the engine without controlling air-supply and exhaust throttle valves to be narrowed down, i.e. to lower thermal efficiency in the engine and while avoiding the deterioration of fuel economy.

The exhaust gas aftertreatment device of the diesel engine is configured so that a heat transmission member which receives the heat of an exhaust gas which has passed the DPF is mounted downstream of the DPF, a heat release member which releases the heat that has been transmitted from the heat transmission member is mounted in the exhaust gas inlet portion of the DOC, the heat transmission member and the heat release member are connected with each other via a thermal conductor thermally insulating relative to the outside, the heat that has been received by the heat transmission member is preserved in the thermal conductor and supplied to the heat release member, and the heat is consequently released from the heat release member into the exhaust gas in the inlet portion of the DOC.