In a spark-ignition internal combustion engine in which a protrusion including an intake-side inclined surface and an exhaust-side inclined surface is formed on a top surface of a piston, and a cavity is formed in the protrusion at a position associated with a spark plug, the intake-side inclined surface and the exhaust-side inclined surface are formed in such a way that an angle defined by an orthogonal plane orthogonal to a center axis of a cylinder and the exhaust-side inclined surface) is smaller than an angle defined by the orthogonal plane and a valve head bottom surface of an exhaust valve, and an inclination angle difference between the exhaust-side inclined surface and the valve head bottom surface of the exhaust valve is larger than an inclination angle difference between the intake-side inclined surface and a valve head bottom surface of an intake valve by 3 degrees or larger.