PURPOSE: To achieve layer formation by eliminating vortex in a cylinder inhibiting layer formation of a mixture in the case of a rotary piston engine provided with a fuel injection valve for directly injecting a fuel from a fuel injection port opened on an air cylinder inner wall surface into a combustion chamber.

CONSTITUTION: Before fuel injection by a fuel injection valve 8, air is injected to the surface of a rotor 3, and an air injection port 19 for eliminating vortex generated in a combustion chamber 9 is provided on the inner circumferential surface of the leading side of a fuel injection port 25 of a rotar housing 1.