Abstract: A process and an apparatus for automatically positioning a piece on a worktable. A worktable (4) supports a reference system (3) constituted by three rollers (G1, G2, G3). The piece such as a substrate (2) is placed on the table (4) in the neighborhood of the rollers. A first pivoting arm (21) comes into contact with a side (C3) of the substrate (2) to bring the opposed side (C1) in contact with the rollers (G1, G2). A second pivoting arm (20) comes into contact with the side (C4) of the substrate (2) to bring the opposed side (C2) in contact with the roller (G3). The arms (20, 21) are controlled by a single means such as a jack (22) of which the body (23) and the rod (24) are floatingly mounted and are respectively associated with the two arms (20, 21). The invention is primarily useful for positioning of a support for integrated circuits in a serigraphic machine.