PURPOSE: To rapidly form concentric folds on a web without exposing this web to a danger of wrinkling the web by providing two set of feedable cam shape bending devices having a social structure.

CONSTITUTION: The cams 3 of respective sets 1 and 2 of the feedable cam shape bending devices 3 are parted at a distance about twice the distance between the bending points of the web and are so arranged as to respectively act on the one side of the web and the other side of the web. The cams 3 of the two sets 1 and 2 are deviated at a distance equal to the distance between the adjacent two bending points of the web and are so arranged to increasingly overlap on each other that the plural folds are simultaneously formed over the distance at which the length thereof corresponds to the web length of the plural folds when the web is fed between the cams 3. In addition, the cams are so constituted as to be rapidly removed from the bent web propelling beyond the distance at which the cams overlap increasingly on each other in such a manner that the web may be further propelled within the machine independently from the cams 3.