PURPOSE: To generate a high torque by operating an exhaust port opening/ closing means while opening a suction port provided by boring at the lower side of a cylinder so as to carry out a two-cycle operation in a low speed full load condition of an engine, and converting to the four-cycle operation in a high speed and in a low speed partial load condition.

CONSTITUTION: Plural suction ports 12 are provided by boring to a cylinder sleeve 11 responding to near the upper side of a piston head 21 at the bottom dead center position of a piston 2, and a sleeve valve 3 is fitted around the sleeve 11 to cover these suction ports 12. To the sleeve valve 3, plural openings 31 are provided by boring responding to the suction ports 12, and permanent magnets 32 are provided at specific two positions of the sleeve valve 3. And fixed electromagnets 41 and 42 to be the rotating means of the sleeve valve 3 are provided responding to the permanent magnets 32. And the suction ports 12 are opened while an exhaust valve 6 is opened and closed in a low speed full load condition to carry out a two-cycle operation, and on the other hand, the suction ports 12 are closed while the suction and exhaust valves 5 and 6 are opened and closed in a high speed and in a low speed partial load condition to carry out the four-cycle operation.