Abstract: In an internal combustion engine including a combustion chamber in a cylinder, an intake port communicated with the combustion chamber at an upper portion of the cylinder, and an intake valve for controlling intake air which flows from the intake port into the combustion chamber at the upper portion of the cylinder, the intake port turns around a valve shaft of an intake valve in a spiral shape so as to produce swirls in the cylinder. The axis of the intake valve is positioned at the plane passing the central axis of the cylinder. The axis of the major intake air flow at an entrance of the intake port is positioned at one side of or out of the plane. The axis of the major intake air flow extends to intersect an inner turning wall of a turning portion of the intake port. The inner turning wall further passes the plane from the one side of the plane to the other side of the plane.