PURPOSE: To certainly weld even a ribbon slight in the content of a thermoplastic substance by supporting at least one cutting underlay stand and a welding underlay stand between roller tables in a longitudinally slidable manner and providing a centrally positionable and height regulable sonotrode above the cutting underlay stand and further providing a guide path equipped a partial notch for allowing a vacuum to act.

CONSTITUTION: A ribbon 7 is inserted so that one end part thereof enters an opposed guide path 5' and the other end part thereof enters other opposed guide path 5. Herein, a vacuum is applied to notches 6, 6' and the ribbon is expanded perfectly flatly in this region under the applied vacuum to be held to a flat state. A cutting anvil 10 is moved in a -X axis direction and an welding anvil 12 follows this movement to come into contact with the lower part of an overlap position 9. A sonotrode 1 is loaded with ultrasonic waves to move in an acting direction W from its start position so as to form an inner space 0.58-1.5 times the thickness of one ribbon between the welding anvil 12 and the sonotrode 1 in a mechanical contact part direction.