A cylinder head and a four-stroke and two-valve spark-ignition internal combustion engine spark-ignition internal combustion engine are provided which allows for enhancing the output and the rotational speed of the engine by increasing the flame propagation rate of the burning air-fuel mixture. As the piston 4 moves up toward the top dead center, the air-fuel mixture within the squish area 14 is inducted along the squish guide groove 15 toward the ignition electrode 7a of the ignition plug 7 and is then ignited by the ignition electrode 7a when the piston 4 approaches the top dead center. When the mixture is ignited by the ignition electrode 7a, there is a flow of the air-fuel mixture around the ignition electrode 7a (the ignition plug aperture 12) inducted by the squish guide groove 15 so as to move toward the center of the combustion chamber, so that the flame propagation rate within the combustion chamber may be enhanced as the ignition is effected on such moving air-fuel mixture.