A welding head comprises a welding element for welding a lid to an opening device of a container, a supporting body for supporting the welding element and a compensating device for compensating a possible mutual mispositioning of the welding element and the lid during welding of the lid to the opening device, the compensating device being interposed between the supporting body and the welding element, the compensating device comprising a planar spring arrangement provided with at least one planar spring element having a first member and a second member mutually connected by deformable elements.