An intake air control device includes: an intake air flow channel that includes an air flow pipe furcated into multiple branch flow channels that communicate with the same combustion chamber; an intake air valve provided to the air flow pipe to adjust an opening degree of the air flow pipe in accordance with a rotation angle thereof; a swirl valve provided to any one of the multiple branch flow channels to adjust an opening degree of the branch flow channel in accordance with a rotation angle thereof; and a cam plate that is rotatable and has a first cam slot. The intake air valve has a first protrusion inserted in the first cam slot. The first cam slot has a first rotation section within which the first protrusion slides and rotates about the rotational shaft of the intake air valve in response to rotation of the cam plate.