An internal combustion engine including two intake valves for each cylinder comprising: - a fixed cam for driving one of the two intake valves with a lift characteristic having a valve opening timing close to a top dead center; - a variable valve actuation mechanism capable of changing, in accordance with an engine running condition, lift characteristics between: - a low-lift characteristic having an event angle and a lift amount each being smaller than an event angle and a lift amount of the fixed cam, - a high-lift characteristic having the event angle and the lift amount each being larger than the event angle and the lift amount of the fixed cam, and - a lift characteristic having the event angle and the lift amount in medium degrees between the low-lift characteristic and the high-lift characteristic; and - a rocker cam for driving another of the two intake valves, to generate a swirling flow, the rocker cam including the variable valve actuation mechanism, wherein the variable valve actuation mechanism is configured - to set the lift characteristic of the rocker cam so as to obtain a valve opening timing on a retard side relative to the valve opening timing of the fixed cam in a case of the low-lift characteristic, - to obtain a valve opening timing that is advanced as the lift characteristic changes toward the high-lift characteristic, and - to obtain a valve closing timing on the retard side relative to a valve closing timing of the fixed cam in a case of the high-lift characteristic. - a fixed cam for driving one of the two intake valves with a lift characteristic having a valve opening timing close to a top dead center; - a variable valve actuation mechanism capable of changing, in accordance with an engine running condition, lift characteristics between: - a low-lift characteristic having an event angle and a lift amount each being smaller than an event angle and a lift amount of the fixed cam, - a high-lift characteristic having the event angle and the lift amount each being larger than the event angle and the lift amount of the fixed cam, and - a lift characteristic having the event angle and the lift amount in medium degrees between the low-lift characteristic and the high-lift characteristic; and - a low-lift characteristic having an event angle and a lift amount each being smaller than an event angle and a lift amount of the fixed cam, - a high-lift characteristic having the event angle and the lift amount each being larger than the event angle and the lift amount of the fixed cam, and - a lift characteristic having the event angle and the lift amount in medium degrees between the low-lift characteristic and the high-lift characteristic; and - a rocker cam for driving another of the two intake valves, to generate a swirling flow, the rocker cam including the variable valve actuation mechanism, - to set the lift characteristic of the rocker cam so as to obtain a valve opening timing on a retard side relative to the valve opening timing of the fixed cam in a case of the low-lift characteristic, - to obtain a valve opening timing that is advanced as the lift characteristic changes toward the high-lift characteristic, and - to obtain a valve closing timing on the retard side relative to a valve closing timing of the fixed cam in a case of the high-lift characteristic.