PURPOSE: To improve quick ignitability and combustibility of intake mixture, in a four valve type internal combustion engine provided with two intake ports and two exhaust ports against one combustion chamber.

CONSTITUTION: In a combustion chamber 5, a protrudent part 18 to divide the combustion chamber 5 into a first combustion chamber 5a comprising one intake port 6 and one exhaust or 8 and a second combustion chamber 5b comprising the other intake port 7 and the other exhaust port 9 is provided. The underside of the protrudent part 18 is formed in a squish area 10 against the top face of a piston. The one intake port 6 is constituted into a tumble port by which intake mixture from the intake port 6 is given loop-like swirl in the vertical direction. Meanwhile, the other intake port 7 is constituted into a swirl port by which intake mixture from the intake port is given loop-like swirl in the lateral direction.