PURPOSE: To enable cooling and lubricating by using oil in a rotary valve by carrying out air cooling by feeding air, by a cooling fan to the outer frame of a heated rotary valve, providing projecting/recessed parts to the outer frame of the rotary valve, or radiating cooling water by a radiator and the like passing cooling water through the outer frame of the rotary valve.

CONSTITUTION: A projecting/recessed part is provided on the outer frame 7 of a rotary valve in a gasoline engine in which an intake rotary valve 1 and an exhaust rotary valve 2 are used. Cooling water 8 is thermally radiated by a radiator 9. Oil 14 for cooling and lubricating of only the rotary valve is cooled by an oil cooler 13. In the engine, ignition is carried out by a plug 5 so as to operate a piston 6. Air cooling or water cooling of the outer frame of the rotary valve leads to cool the rotary valve. Engine oil is lubricated on the rotary valve, and cooled by an oil cooler and the like so as to cool and lubricate the rotary valve. It is thus possible to reduce the degree of stain of oil, and also suppress any scratch on the rotary valve.