PURPOSE: To enable an optimum swirl ratio and a high coefficient of discharge by connecting one of the two intake ports opening into a cylinder to the terminal part of the other, and then setting the size of a connection opening at the terminal part of the other into a specific percentage of the cross-sectional area of the one.

CONSTITUTION: At a state where a cylinder head 10 is attached to a cylinder block, both two intake ports 11, 12 and two exhaust ports 13, 14, which are opening into a cylinder, are arranged appropriately on the circumference of a nozzle mounting hole 15. In addition, one of the two intake ports 11, 12 is formed into a directional port 11, and the other into a helical port 12 respectively, and at the same time, the directional port 11 is connected to a swirl chamber 22 as the terminal part of the helical port 12. Hereupon, the connection opening 23 within the swirl chamber 22 of the helical port 12 is set into a size 10W80% of the passage cross-sectional area of the directional port 11 at a place to which the helical port 12 is connected.