Provided is a dual venturi having: a tubular part; a body part, for opening/closing the flow of secondary air by rotating in the horizontal plane and vertical plane directions, the horizontal plane direction being the cross-sectional direction of the tubular part and the vertical plane direction being perpendicular to the horizontal plane; a central passageway, becoming the passageway for primary air; a damper part, and a damper part-side secondary gas outlet; a driving part, for rotationally driving the damper part in the horizontal and vertical planes; a gas inlet-side primary gas outlet connected openly to the damper part-side primary gas outlet; and a gas inlet for introducing gas into the tubular part via the damper part, which openly connects selectively to the damper part-side secondary gas outlet on the basis of the rotational position of the damper part, and for forming the rotational shaft of the damper part along with the rotational shaft of the driving part.