A dual venturi for a combustion device, the dual venturi comprising: a housing having at one side thereof a discharge part coupleable to a turbo fan, and in an interior thereof a predetermined space for allowing gas and air to flow; an air supply unit defined in the inner side of the housing and divided by a first partition into a first air supply unit and a second air supply unit; a gas supply unit provided on one side of the housing and divided by a second partition into a first gas supply unit having a first opening so as to communicate with the first air supply unit and a second gas supply unit having a second opening so as to communicate with the second air supply unit; and an opening and closing unit configured such that when the combustion device needs a low quantity of heat, the opening and closing unit blocks both the second air supply unit and the second opening, thereby blocking a flow of secondary air and secondary gas, and when a high quantity of heat is needed, the opening and closing unit opens both the second air supply unit and the second opening, characterized in that, the opening and closing unit comprising: a motor provided outside the housing; a damper combined with the motor, the damper being provided with at least two concave guides and convex guides on an inner surface thereof; a movable body having concave guides and convex guides that are correspondingly engaged respectively with the concave guides and the convex guides of the damper; and a valve body combined with a center of the movable body, and opening and closing the second opening in response to movement of the movable body, wherein the motor further includes a limit switch to rotate the damper at a 90 degrees angle. a housing having at one side thereof a discharge part coupleable to a turbo fan, and in an interior thereof a predetermined space for allowing gas and air to flow; an air supply unit defined in the inner side of the housing and divided by a first partition into a first air supply unit and a second air supply unit; a gas supply unit provided on one side of the housing and divided by a second partition into a first gas supply unit having a first opening so as to communicate with the first air supply unit and a second gas supply unit having a second opening so as to communicate with the second air supply unit; and an opening and closing unit configured such that when the combustion device needs a low quantity of heat, the opening and closing unit blocks both the second air supply unit and the second opening, thereby blocking a flow of secondary air and secondary gas, and when a high quantity of heat is needed, the opening and closing unit opens both the second air supply unit and the second opening, characterized in that, the opening and closing unit comprising: a motor provided outside the housing; a damper combined with the motor, the damper being provided with at least two concave guides and convex guides on an inner surface thereof; a movable body having concave guides and convex guides that are correspondingly engaged respectively with the concave guides and the convex guides of the damper; and a valve body combined with a center of the movable body, and opening and closing the second opening in response to movement of the movable body, a motor provided outside the housing; a damper combined with the motor, the damper being provided with at least two concave guides and convex guides on an inner surface thereof; a movable body having concave guides and convex guides that are correspondingly engaged respectively with the concave guides and the convex guides of the damper; and a valve body combined with a center of the movable body, and opening and closing the second opening in response to movement of the movable body,