The welding unit, in particular, for ultrasonic welding is designed as an electrode holder (1) with arms (2, 3) and an operating device (20) for opening and closing the arms. The device (20) incorporates a base element (23) on the arm (3) and a displacement element (25) on the arm (2). The arm (3) is movably installed by means of a slideway (11). The bearing unit (10) and the slideway (11) are designed so that both arms (2, 3) are displaceable together to engage the workpiece to be welded.
