A plate material processing system comprising a plate material processing machine to perform processing on an unprocessed plate material and a loader to load the unprocessed plate material into the plate material processing machine, wherein the plate material processing machine includes: a processing head to perform processing on the unprocessed plate material; a table on which the unprocessed plate material is to be placed; and a plate material moving mechanism to move a plate material on the table forward, backward, leftward, and rightward, wherein the plate material moving mechanism includes: a carriage that is movable forward and backward; and a work holder, mounted to the carriage so as to be movable leftward and rightward, to hold a front end portion of the unprocessed plate material, the loader includes: a plate material attaching unit capable of attaching to the unprocessed plate material, characterized by a pivoting mechanism to pivot the plate material attaching unit on a predefined arc-shaped trajectory while maintaining the plate material attaching unit in a constant orientation as viewed in a planar manner, wherein in operation the pivoting mechanism shifts the plate material attaching unit on the arc-shaped trajectory between an unprocessed plate material loading position and an unprocessed plate material waiting position, the unprocessed plate material loading position being on a portion of the table, which portion is positioned forwardly of the processing head and on one side of the table in a leftward-rightward direction, the unprocessed plate material waiting position being positioned on the one side of the table and backwardly of the unprocessed plate material loading position, when the plate material attaching unit is at a foremost position, on the arc-shaped trajectory, between the unprocessed plate material loading position and the unprocessed plate material waiting position, the plate material attaching unit is positioned so as to interfere with the work holder that is positioned on the one side in a range in which the work holder is movable leftward and rightward in a state where the carriage is at a foremost position in a range in which the carriage moves forward and backward, and when the plate material attaching unit is at the foremost position, the plate material processing machine positions the work holder to the other side of the left and right sides relative to the processing head, away from the unprocessed plate material loading position side. a processing head to perform processing on the unprocessed plate material; a table on which the unprocessed plate material is to be placed; and a plate material moving mechanism to move a plate material on the table forward, backward, leftward, and rightward, wherein the plate material moving mechanism includes: a carriage that is movable forward and backward; and a work holder, mounted to the carriage so as to be movable leftward and rightward, to hold a front end portion of the unprocessed plate material, a plate material attaching unit capable of attaching to the unprocessed plate material, characterized by a pivoting mechanism to pivot the plate material attaching unit on a predefined arc-shaped trajectory while maintaining the plate material attaching unit in a constant orientation as viewed in a planar manner,