A control device for gas is provided with a pivotable flap mounted between side walls of a guide duct. A receiving pocket for the insertion of a drive element (motor) is provided on one of the side walls and is oriented in such a way that, after insertion, the output shaft of the drive element is in engagement with the flap. This receiving pocket may be arranged so that the drive element is inserted coaxially with respect to the pivot axis of the flap or transversely thereto, or if the receiving pocket extends into the interior of the duct, the pivot flap is provided with a corresponding cut-out.