Abstract: In a machine for driving a fastener, e.g. a nail, a staple or the like by one impact blow into an object by means of a driver actuating the fastener and connected to one end of a bar-shaped spring which extends between a plurality of spring supports, said supports being distributed throughout the length of the spring and said driver being reciprocable in a tensioning stroke for tensioning and bending the spring about at least one of the supports and in a striking stroke generated by the tensional force of the spring for driving the fastener into the object, the invention provides the improvement that at least one of the supports is adjustable for regulating the tensional force of the spring in order to control the energy released in the striking stroke.