To provide a diesel engine for low volatile fuel to improve fluidity of air and fuel through injection of fuel in a cylinder at the initial stage of a compression stroke and suppress the generation of NOx through the generation of uniform air-fuel mixture.

A diesel engine is formed such that an auxiliary combustion chamber 2 is formed in a piston 5a main combustion chamber 1 consists of a combustion chamber structure 3 arranged in the cavity 9 of a cylinder head 7. At the initial stage of a compression stroke, low volatile fuel, such as heavy oil, is injected in a cylinder 8 through a fuel injection nozzle 6 and dispersed in swirl present in the cylinder 8. Uniform air-fuel mixture of fuel and air is generated in the cylinder 8 and at the terminal state of the compression stroke, the air-fuel mixture penetrating through a communication hole 15 is ignited and burnt in the auxiliary combustion chamber 2 by the aid of a glow plug 4.