Provided is a joint jig of a spiral duct manufacturing apparatus including an uncoiler around which a metal plate member is wound; a wave bending device which cuts the metal plate member supplied from the uncoiler into a straight line and waves and forms a single folded portion and a double folded portion at both edges of the cut metal plate member; a ball caster which bends the projecting wave portions of the metal plate member supplied from the wave bending device upward; a pair of transfer rollers which transfer the metal plate member supplied through the ball caster; upper and lower pressing rollers which are installed adjacent to each other in the vertical direction and press the single folded portion and the double folded portion of the metal plate member; and upper and lower cutters which cut a spiral duct pressed by the upper and lower pressing rollers. The joint jig is installed on the front surface of the upper and lower pressing rollers so as to form the metal plate member, transferred by the transfer rollers, into a cylindrical shape. As the joint jig is installed in the spiral duct manufacturing apparatus, an elbow can be easily manufactured. When the elbow is manufactured, the elbow can be freely moved. Therefore, there is no trouble in forming the elbow.