Abstract: A preliminary assembly system for joining a body side panel and a floor panel of an automotive vehicle in a loose-fit hemming joint state by bending a claw piece extending from a main body of one of the panels to hold the other of the panels, prior to welding. The preliminary assembly system comprises a die to be in contact with a back-side surface of the main body of one of the panels in a region forming a loose-fit hemming joint section. Additionally, a main bending blade is provided to be movable to approach the die to bend the claw piece until the loose-fit hemming joint state is established. The main bending blade is moved to approach the die by a movement amount which is mechanically determined relative to a surface of the other of the panels during formation of the loose-fit hemming joint section.