A vertical Pittsburgh Seam closing apparatus having a base supporting surface, a track mechanism for moving a carriage assembly which holds seam forming members used to close a Pittsburgh Seam, a pair of upper and lower guide members for guiding the duct section into a proper vertical position, and upper and lower clamping members positioned inside the duct section and adjacent the inside portion of the Pittsburgh Seam to be closed, the upper guide members and clamping member being selectively movable and adjustable for accommodating different duct section lengths. In one embodiment, the seam forming assembly includes three roller members mounted in vertical arrangement to each other, one roller member being V-shaped in configuration and the other two roller members being substantially cylindrical in shape. The V-shaped roller member may also include one or more projecting members for forming dimples in the closing process to prevent shifting and/or slipping of the closed seam.