An ultrasonic processing system, including first and second mechanical elements (67, 68) configured to subject a web continuously running in a machine direction to ultrasonic processing, the first and second mechanical elements (67, 68) face each other across the web in a thickness direction of the web, wherein: the ultrasonic processing system further includes an upstream side conveying means and a downstream side conveying means for continuously feeding the web in the machine direction; a drum having an outer peripheral surface adapted to rotate continuously at the same circumferential velocity as a running velocity of the web and adapted to support the web on the outer peripheral surface is disposed between the upstream side conveying means and the down-stream side conveying means; the outer peripheral surface is provided with a ultrasonic processing portion communicating with an inner side as well as an outer side of the drum; the first mechanical element configured to be repetitively moved forward and backward in a direction intersecting with the machine direction across the web is disposed on the inner side of the ultrasonic processing portion of the drum; the second mechanical element configured to be repetitively moved forward and backward together with the first mechanical element is disposed on the outer side of the ultrasonic processing portion of the drum; and wherein the first mechanical element and the second mechanical element cooperate with each other to subject the web positioned in the ultrasonic processing portion to ultrasonic processing in the both steps of moving forward and moving backward but respective home positions of the first and second mechanical elements (67, 68) are drawn apart from each other after completion of the ultrasonic processing in the two steps. the ultrasonic processing system further includes an upstream side conveying means and a downstream side conveying means for continuously feeding the web in the machine direction; a drum having an outer peripheral surface adapted to rotate continuously at the same circumferential velocity as a running velocity of the web and adapted to support the web on the outer peripheral surface is disposed between the upstream side conveying means and the down-stream side conveying means; the outer peripheral surface is provided with a ultrasonic processing portion communicating with an inner side as well as an outer side of the drum; the first mechanical element configured to be repetitively moved forward and backward in a direction intersecting with the machine direction across the web is disposed on the inner side of the ultrasonic processing portion of the drum; the second mechanical element configured to be repetitively moved forward and backward together with the first mechanical element is disposed on the outer side of the ultrasonic processing portion of the drum; and wherein the first mechanical element and the second mechanical element cooperate with each other to subject the web positioned in the ultrasonic processing portion to ultrasonic processing in the both steps of moving forward and moving backward but respective home positions of the first and second mechanical elements (67, 68) are drawn apart from each other after completion of the ultrasonic processing in the two steps.