Abstract: Apparatus for turning by 90.degree. a panel or a panel stack (P) on a cutting machine worktable (Q) comprises a withdrawable gripper means (1) rotatable about a vertical axis (2), which upon control clamps a panel stack (P) close to one of its rear corners. The gripper (1) is associated with a carriage (7) for causing the gripper (1) to perform in a programmable precise manner a rectilinear movement (3) near to, and away from the cutting line (Z) of the longitudinally cutting machine, such that the panel stack (P) will be turned in a clockwise or counterclockwise direction, depending whether it is clamped at its left-hand or right-hand corner. A withdrawable push roller (4) acts on the panel stack (P) concurrently with the gripper by being moved parallel to the longitudinally cutting machine in a programmable precise manner, so that it assists in the desired turning of the panel stack (P).