Abstract: The invention relates to an apparatus for mechanically joining metal sheets which lie flat one upon the other, having a tool set comprising at least one punch and one die which bounds a cavity in which the joining operation takes place, the punch displacing sheet-metal material out of a sheet-metal plane and upsetting it, and at least one tool part being arranged, for this purpose, on a displaceable tool carrier which has a holding-down means supported in a spring-prestressed manner adjacent to the tool part. In order that the holding-down means allows high outputs, it is provided that, for the spring prestressing of the holding-down means, the tool carrier has a cylinder cavity in which there is guided a piston which acts on the holding-down means and on the head side bounds, with volume-changing action, a pressure chamber which can be subjected to the action of a fluid pressure medium.