PURPOSE: To prevent knocking of a high compression ratio internal combustion engine by constituting a cylinder therefor such that it is provided with a recess formed on that portion of its inner face which defines a combustion chamber at an initiation of a piston lowering stroke in order to increase the volume of the combustion chamber at the initiation of a combustion stroke to decrease the combustion pressure rising rate therein.

CONSTITUTION: In a high compression ratio Diesel internal combustion engine in which a main combustion chamber 6 is defined by a cylinder head 3 and the top face of a piston 5, an annular recess 11 having an upper end section 11a and a lower end section 11b is formed at a portion of a cylinder 2 somewhat below the top dead center position T of the piston 5.