A two-stroke engine comprising three exhaust valves and two intake valves. These exhaust valves and these intake valves are arranged on the peripheral portion of the inner wall of the cylinder head, and one additional intake valve is arranged on the central portion of the inner wall of the cylinder head. The valve openings of the three intake valves, which are located on the exhaust valves side, are masked by the masking walls. The central portion of the combustion chamber is scavenged by the fresh air fed from the additional intake valve, and the peripheral portion of the combustion chamber is scavenged by the fresh air fed from the remaining two intake valves.