Internal combustion engine

The utility model relates to an internal combustion engine which facilitates combustion of mixed gas to save oil consumption. The top surface (18A) of a piston (18) comprises a recess (29) and a gas-inlet side gas extrusion portion (30). In the state that the piston (18) is close to a top dead center, the recess (29) upwards forms an opening shape in the center of the top surface (18A) in a mode of enclosing a firing point (P1) of a spark plug (PL). The bottom surface of the recess (29) is higher than the gas-inlet side gas extrusion portion (30). The gas-inlet side edge portion (38A) of the recess (29) is lower than an exhaust side edge portion (38B). In a compression stroke, due to the fact that the volume between the gas-inlet side gas extrusion portion (30) and the lower surface (16A) of a cylinder head (16) opposite to the gas-inlet side gas extrusion portion (30) becomes smaller, and the gas-inlet side gas extrusion portion (30) serves as a portion for generating an extruded gas flow (S) which enables t