To provide a method for increasing real amount of air-fuel mixture in a cylinder when an engine b is in a compression process and increasing explosion rotational speed of the engine from low speed rotation toward high speed rotation.

Size of a valve f is reduced for a valve e of the engine b. Timing for closing the valve f is quickened from low speed rotation time toward high speed rotation time in a compression process. An opening and closing device is mounted in a space having nothing from the valve (a passage ((a pipe)) to a part where air-fuel mixture remains temporarily) to increase amount of closing when explosion rotational speed of the engine is from low speed rotation time toward high speed rotation time.