A cylinder head of an engine body is provided with intake ports and exhaust ports, which are connected with and opened to a combustion chamber. The intake ports are disposed in one of right and left sides of the cylinder head with respect to a vehicle driving direction, and the exhaust ports are disposed in the other of the right and left sides of the cylinder head. An intake pipe 61 passes around the cylinder head 31 at a side of the engine body, therefore, a curved portion 63 is formed in the intake pipe. A larger amount of fresh air enters the combustion chamber from one intake port than the other intake port, thus swirl occurs in the combustion chamber. An injector that injects fuel into the intake pipe is positioned at a side of the intake pipe.