A dual venturi having a tubular part having primary and secondary passageways, wherein a primary gas inlet is provided on the side wall of the primary passageway; a body part, for opening/closing the flow of secondary air by rotating in 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 damper part having a damper part-side secondary gas outlet; a driving part, for rotationally driving the damper part in the horizontal and vertical planes; and a secondary gas inlet, 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.