PURPOSE: To obtain high suction air charging efficiency and heat regenerating efficiency by providing a regenerator within a cylinder head and providing an exhaust valve in an exhaust port which passes through said regenerator.

CONSTITUTION: A suction port 2a which is opened and closed by means of a suction valve 2, is provided in a cylinder head 10, while an exhaust passage 18 which is opened and closed by means of an exhaust valve 1, is provided inside the cylinder head 10. An annular recess or chamber 22 is provided on the outer wall face of the cylinder head 10 in such a way that it surrounds the end part of the exhaust passage 18, with its opening end being closed by a cover 20. And, an annular regenerator 3 is housed in the chamber 22, which is connected to a sub-chamber 21 while also connected to the end part of a cylinder 11 through a connecting passage 15. In the central part of the cover 20 is provided a fuel injection nozzle 4, which injects fuel into suction air which is heated by heat accumulated in the regenerator 3.