An object is to provide a diesel engine (2) capable of reliably preventing an excessive rise in temperature inside a particulate filter (10) and capable of rapidly enabling driving in a low-rotation and low-load area when there is no possibility of excessive rise in temperature. A diesel engine (2) includes a diesel engine (2) exhaust emission purifier (1). The diesel engine (2) exhaust emission purifier (1) includes a particulate filter (10) and a controller (21) for forcibly removing a particulate accumulable in the particulate filter (10). The controller (21) is configured to prohibit the diesel engine (2) from entering a predetermined low-rotation and low-load area if a load rotation changes when the particulate filter (10) has a temperature that is equal to or higher than a first predetermined temperature T1 and when the particulate is accumulated in an amount that is equal to or more than a predetermined amount.