PURPOSE: To eliminate a need for a conventional valve mechanism and to remarkably simplify constitution by a method wherein a piston stoker to open and close suction and exhaust ports rotated in linkage with stroke movement of a piston is arranged inside a cylinder.

CONSTITUTION: A piston 5 reciprocated by coupling rod-crank systems 6 and 6a is fitted in a cylinder 1 having a head part being closed by a head 2 arranged at an ignition plug 3. In this constitution, a stoker 5 separated from a cylinder 1 is intervened between the cylinder 1 and the piston 5. The stoker 5 is provided at an upper end with a ring 5a and at a lower end with a belt 5b. The ring and the bell are rotatably engaged with a notch 1a and a bell-form flare 1b formed in the two ends of the cylinder 1. A bevel gear 11 arranged at the lower end of the stoker 5 is engaged with a bevel gear 11a arranged on a crank shaft 6a. By rotating the stoker 5 in linkage with engine movement, an exhaust port 9 is opened and closed.