An apparatus for continuously bonding and/or welding material webs by means of ultrasound, having an ultrasonic horn configured as a rotating roller, an anvil radially opposite the rotating roller, an amplitude transformer set axially on the rotating roller, an ultrasonic converter attached to the amplitude transformer with an energy supply, where the length 1 of the rotating roller equals a .lamda./2 wave or a multiple thereof (1=x.lamda./2).