A workpiece placement platform device including: an X-axis direction positioning member provided on one side of a placement platform on which to place a plate-shaped workpiece and configured to position one side edge of the workpiece in an X-axis direction by contacting the one side edge; a Y-axis direction positioning member provided on another side of the placement platform and configured to position another side edge of the workpiece in a Y-axis direction by contacting the another side edge; and a workpiece positioning member that is movable in and out relative to a workpiece placement surface of the placement platform and configured to partition the workpiece placement surface into sections in the X-axis direction and enable simultaneous positioning at the sections on the workpiece placement surface.