The present invention relates to an apparatus for producing a gathered material, wherein the material consists of two material web portions and a thread positioned between the material web portions and the two material web portions are connected to one another at two connecting surfaces, wherein the thread is disposed between the two connecting surfaces such that the thread is connected to the material web portions, wherein the apparatus comprises a sonotrode having a first sealing surface and a counter tool having a second sealing surface, wherein the counter tool is cylindrical with a lateral surface and a cylinder axis and the second sealing surface is disposed on the lateral surface, wherein the sonotrode and the counter tool are disposed with respect to one another in a processing position such that the material web portions and the thread can be guided through a gap formed by the first and the second sealing surface in a feed direction tangential to the lateral surface of the counter tool. To overcome or at least mitigate the described drawbacks, it is proposed according to the invention that the sonotrode comprise a groove which is oriented in feed direction and extends over the entire first sealing surface for receiving the thread.