This invention relates to an in-cylinder injection internal combustion engine. A recessed portion (22A) is arranged in a top wall of a piston (22) to promote formation of a vertical swirl so that a flow of inducted air introduced into a combustion chamber (27) of the engine is caused to advance from a lower wall (21A) of a cylinder head (21) of the engine toward the top wall of the piston (22) and then to advance backward from the top wall of the piston (22) toward the lower wall (21A) of the cylinder head (21). A corner of the recessed portion (22A) is formed blunter at an outlet side of the vertical swirl than at an inlet side of the vertical swirl. In the in-cylinder injection internal combustion engine in which fuel is injected directly into the combustion chamber (27), it is possible to achieve inter alia a high gas mileage by allowing a lean air-fuel mixture to undergo stratified combustion and also a high power output when a gas-fuel mixture richer than the lean air-fuel mixture is burnt. A high-efficiency internal combustion engine can hence be provided.