A diesel engine includes: a PM filter provided in its exhaust passage; a fuel injection valve for performing post fuel injection in a cylinder of an engine body in addition to primary fuel injection, in order to supply fuel to the PM filter, to maintain its purification performance; an oil level sensor for detecting a degree of dilution of engine oil; and a first indicator lamp that is turned on to indicate that the engine oil needs to be changed when the degree of dilution of engine oil detected by the oil level sensor is equal to or greater than an allowable level. The vehicle diesel engine overrides the prohibition of the post fuel injection until a distance traveled by the vehicle after the indicator lamp is turned on reaches a predetermined distance.