A stitching apparatus for manufacturing stitching wire staples, in particular annular eyelet staples, for stitching stacked sheet materials, includes a stitching head basic body having a driver for driving the stitching wire staples into the stacked sheet materials in a downward movement of the driver. A former shapes the stitching wire staples, in particular annular eyelet staples. The former is pivoted away during the downward movement of the driver. A wire clamping lever is mounted pivotably in the former. The wire clamping lever has a control element which runs on a control cam in such a way that the former is supported as a result in the upward movement of the driver, with the result that the former is pivoted-in in the upward movement to a different point than the pivoting-out of the former in the downward movement.