In a movable sawing unit for severing planar workpiece panels, which has a severing blade and a prescoring saw blade for cutting a prescore groove to prevent splintering of panels by the severing blade, a device for adjusting the depth of penetration of the prescoring saw blade. The prescoring saw blade is operably positioned in advance of the severing blade, upon a vertically movable support. A tactile element associated with the vertically movable support moves along a directing surface extending along the direction of advance of the workpiece panel, causing the prescoring saw blade to occupy a plurality of cutting positions.