PURPOSE: To make the quality of each blank uniform and to eliminate the waste of materials by blanking the blank to form with bend a box main body from a strip plate so as to coincide its vertical direction and by blanking the blanks for top plate and bottom plate in the width direction of the plate stock.

CONSTITUTION: The plate stock 14 of a colored steel plate, etc. is set to the size of the width A to which two times of the width size B of a flange 9d are added to the height H of a box body 12. The first blank 15 for forming a box main body 9 is blanked so as to coincide the vertical direction of the blank 15 with the width direction of the plate stock 14. The second blank 16 for forming a top plate 10 and the third blank 17 for forming a bottom plate 11 are blanked so as to coincide the width direction of the blanks 16, 17 with the width direction of the plate stock 14. With this stock layout method the inconvenience of varying the quality and color of each blank 15W17 is eliminated. A back plate 13 is formed by a zinc plated steel plate, etc.