PURPOSE: To contrive stabilization of burning by generating a sufficient swirl through a simple structure and lowering fluctuation of burning, by providing a spiral-formed protruded stripe meeting at about right angle with an inclining direction of a suction valve on the wall surface of a combustion chamber inside a cylinder head.

CONSTITUTION: At the time of suction, although air-fuel mixture to be led to a combustion chamber 3 is apt to spread out along a wall surface of the combustion chamber 3 at a bevel part of a suction valve 5, as for a direction A motion of an ingredient of the air-fuel mixture in the direction A is interrupted and attenuated as a protruded stripe 9 is acted upon the mixture as an obstacle and as for a direction B motion of an ingredient of the air-fuel mixture in the direction B is facilitated as the protruded stripe 9 fulfiles a rectifying function at the time of flowing. In consequence of the above, a gas flow in a cylinder 2 turned into a swirl flow in a suction stroke. On the other hand, even at the time of a compression stroke, burning is stabilized by making the swirl flow continue until completion time of the stroke, and burning efficiency is increased by generating microturbulence on the surface of of the protruded stripe through the resistance of the protruded stripe 9.