Provided are an apparatus and method for manufacturing a spiral duct in which straight connection parts are integrally formed with both ends of a curved duct. Further provided are an apparatus and method for manufacturing a spiral duct capable of improving cutting quality of a metal band and precisely and securely coupling bent parts of edges of the metal band. The apparatus comprises a cutting roll to cut a metal band into two parts, the cutting roll having a horizontal rotation angle that can be varied to cut along a straight or a waved line in order to form a duct having straight and curved parts, and in order to adjust a diameter of the duct. In addition, the apparatus includes rolls for forming bent parts at edges of the cut metal bands, and for winding and seaming edges of the metal bands to form ducts.