To avoid the event that an insertion failure occurs between sheets due to the weak resilience of a V-shaped tape piece by pushing and crushing only a central portion of a tape, when folded, to secure sufficient resilience of the V-shaped tape piece.

A folding driving roller 10 is a single roller having a width (an axial length) greater than that of the tape 2. Each of an insertion side thrust roller and a discharge side thrust roller is a single roller having a width for pressing only the central portion against the folding driving roller so that the insertion side thrust roller 11 and the discharge side thrust roller 15 thust only the central portion of the tape in the direction of its width against the folding driving roller.