Abstract: A diesel engine comprising a fuel injection device and a controller for controlling the fuel injection device in accordance with an operating condition of the engine. The fuel injection device effects a preliminary injection for injecting fuel into a cylinder during a period from the initial part of an intake stroke to the middle part of a compression stroke and a main injection for injecting fuel into a combustion chamber in the vicinity of a top dead center of the compression stroke, whereby lean mixture is formed and a maximum combustion temperature in the combustion chamber is decreased to suppress generation of NOx and to reduce emission of black smoke.