Abstract: A parts installing system installs a plurality of parts on a workpiece substantially simultaneously. The system includes a parts stocker for stocking a cluster of substantially closely arranged parts thereon, and a parts transfer device for transferring the parts from the parts stocker to a prescribed position over the workpiece and setting the transferred parts over the workpiece. The parts transfer device includes a parts spreading mechanism unit which picks up the clustered parts from the parts stocker and spreads them into respective relative positions corresponding respectively to relative positions which will be taken by the parts set on the workpiece. The system also includes a pressing device for pressing the parts set over the workpiece onto the workpiece, and a bolt fastening device for fastening the pressed parts to the workpiece with bolts. The parts installing system is suitable for use on various automated production lines to achieve a high rate of production.