PURPOSE: To provide an expandable and elastic product by a method wherein horizontal folds horizontally protruded continuous section are reciprocally formed on one side of two sheets each and the back of each sheet respectively and further, the entire two sheets are reciprocally combined at a free edge of the protruded section.

CONSTITUTION: A first fold 14 is formed on one side of a first sheet 8 and second folds 16 and 17, on the back of each sheet by fold forming devices 22 and 12. The fold 17 is formed so that it may be longer than the fold 16. A structure 10 is preferably of polyester to maintain the folded portion when two sheets are heated and folded. Thereafter, the sheets 10 and 8 are passed through form changing devices 18 and 24 thereby the second fold 17 being changed to be a leg section 20. The folded and form-changed sheets 8 and 10 are junctioned by a junctioning device 26 which results in having a finished product 2 discharged downward.