A plate material processing system includes a plate material processing machine (1) and a loader (2). The plate material processing machine (1) holds a front end portion of an unprocessed plate material (W1) by a work holder (14) and moves the unprocessed plate material (W1) on a table (5) forward, backward, leftward and rightward. The loader (2) includes: a plate material attaching unit (20); and a pivoting mechanism (25) for pivoting the plate material attaching unit (20) on a predefined arc-shaped trajectory (C) while maintaining the plate material attaching unit (20) in a constant orientation as viewed in a planar manner. When the plate material attaching unit (20) is at a foremost position (PF), the work holder (14) is positioned to the other side of the left and right sides relative to a processing head (6), away from the unprocessed plate material loading position (P2) side, thereby preventing the work holder (14) and the plate material attaching unit (20) from interfering with each other.