An exhaust passage for connecting to an exhaust port of a cylinder is provided. The exhaust passage includes a first path extending in a direction generally orthogonal to the central axis of the exhaust port. A second path connects the first path and the exhaust poil and a control valve is provided in the first path. The rotational axis of the exhaust control valve is generally parallel to the direction in which the first path extends. The surface area of an opening connecting the first path and the second path is variable as the exhaust control valve rotates, so as to carry out controlled combustion and exhaust timing. This makes it unnecessary to provide a hollow section for housing an exhaust control valve and bearing at a position close to the exhaust. It is also possible to reduce the size of a cylinder block and to realize smooth flow of exhaust gases by making the inner peripheral surface of the exhaust passage smooth.