The present invention provides a simply-structured ultrasonic processing apparatus 50 for subjecting a fibrous web running in a machine direction to ultrasonic processing in a width direction thereof. In the ultrasonic processing apparatus 50, upstream side conveying means 51 and downstream side conveying means 52 allow a fibrous web 31 to run in a machine direction MD continuously. Between the means 51, 52, a working surface of a first mechanical element serving as a stationary element of the ultrasonic processing apparatus 50 extends diagonally with respect to the machine direction MD. The fibrous web 31 runs in the machine direction MD above the working surface. The ultrasonic processing apparatus 50 includes a second mechanical element adapted to move in a direction diagonally intersecting the machine direction. The working surface of the first mechanical element cooperates with the second mechanical element to subject the fibrous web 31 to ultrasonic processing. One of an ultrasonic horn 63 and an anvil 68 is used as the first mechanical element and a remainder of the ultrasonic horn and the anvil is used as the second mechanical element.
