To provide a diesel engine quickly reducing an air exceeding rate when regenerating a NOx occlusion/reduction catalyst.

The diesel engine comprises a control device 26 for controlling a fuel injection device 9 and an EGR device 19. When an engine operating condition is in a region of lower load/lower rotation than a preset operating condition, the control device 26 sets the EGR rate of the EGR device 19 to be higher than in actualizing diffusion combustion and an air exceeding rate to be lower than in actualizing the diffusion combustion. Thus, fuel is injected earlier than at the compression top dead center of a piston 4 to actualize premixture combustion. When a preset amount of NOx is occluded in the NOx occlusion/reduction catalyst 30 and the engine operating condition is in a region of actualizing the premixture combustion, the control device executes regenerating control to reduce the air exceeding rate with NOx reducing fuel injection in addition to normal fuel injection.