An apparatus and a method for ultrasonic processing improved so as to prevent a fibrous web from being disfigured due to the ultrasonic processing. In an apparatus to ultrasonically process a fibrous web running in a machine direction MD, a first mechanical element defined by one of an ultrasonic horn and an anvil and a second mechanical element defined by the other of the ultrasonic horn and the anvil are moved forward or backward in a direction crossing the machine direction MD so as to pass transversely across the fibrous web.
