Internal combustion engine

To provide an internal combustion engine that can generate a strong swirl by increasing the amount of intake air for generating the swirl in a simple structure. In the internal combustion engine provided with a cylinder head formed with an air intake port having first and second ports, when a second intake valve for opening and closing the second port is brought into a halted state by a valve halting mechanism, a swirl is generated by intake air flowing through the first port in a combustion chamber. At a first inlet slot, the line of intersection between a first plane, which is a plan including the first inlet slot and a first orthogonal plane inclines upwardly as it approaches from the position near the outer periphery of the combustion chamber towards a second reference plane, and the first port includes a port section having a passage shape which extends substantially along a perpendicular line orthogonal to a first plane from the first inlet slot towards the upstream by a predetermined length of the passage in a plan view.