A spark-ignition engine capable of reducing the content of hydrocarbon in exhaust gas is provided. When viewed from a direction parallel to a cylinder center axis, given a central virtual line passing a squish area maximum-width section and the center of a combustion chamber recessed section, and one area a and the other area b divided by the central virtual line, an intake valve port or an exhaust valve port is opened in one area of any opposed section of opposed sections of the combustion chamber recessed section. A spark-plug attachment hole is formed in the other area of the opposed section, such that, when viewed from the direction parallel to the cylinder center axis, a spark discharge section at a tip of a spark plug does not overlap the central virtual line.