PURPOSE: To prevent a louver from breakdown and to continuously perform a series of working stages in a short time by passing a sheet between a pair of 1st gears to make plural notches, continuously passing the sheet between the 2nd gears and bending the sheet between the adjacent notches.

CONSTITUTION: The 1st corrugation gears (a) are composed of a pair of an upper side 1st gear 4 and a lower side 1st gear 5 fixed respectively to a driving shaft 40, 50 driven by a driving motor. The sheet 11 is bent continuously in the corrugated form to carry out the 1st stage making plural notches between the bent parts. The 2nd corrugation gear (b) is composed of a pair of an upper 2nd gear 7 and a lower 2nd gear 8 fixed respectively to drive shafts 70, 80 by the driving motor. The interval between the notches formed on the corrugated sheet 11 is bent to carry out the 2nd stage forming the louver.