PURPOSE: To give the long size coil like as the coil for manufacturing the architectural materials the suitable workability and the material strength, by forming the flods with a specified breadth at a specified interval in the strip.

CONSTITUTION: The Z-section fold 4 is formed at a specified position parallelly to the broad direction A in the strip 3 like as the steel sheet, nonferrous metallic sheet, etc. The fold 4 is pressed from upside and bottom side B to form the flat surface; hereby, the fold 2 with thickness treble of that of the strip 3 is formed. This fold 2 is repeatedly formed at the required interval along the longitudinal direction of the long size strip 3 parallelly to the broad direction A of the strip 3. By coiling this long size strip 3, the long size coil 1 with folds 2 is obtained. According to this method, the long size coil with required strength suitable for the purpose can be simply manufactured.