PURPOSE: To suppress the movement of the side face of a slab to the back surface of a hot rolled steel sheet, to reduce the generation of seam flaws and to eliminate edge folding by forming a semicylindrically curved projecting part in the parallel part of a die.

CONSTITUTION: The parallel part of the die 1 for width press device is shaped into the semicylindrically curved projecting part 3. When the slab 11 is edged with the die 1 having the semicylindrically curved projecting part 3, a semicylindrically curved recessed part 12 is formed on the side face of the slab 11. When the slab 11 is worked into a hot-rolled steel sheet by hot-rolling, plastic deformation is generated. In the metal flow of plastic deformation, the curved recessed part 12 is not spreaded to the outwards the corner parts and the moving amount to the surface and back faces of the hot rolled steel sheet is suppressed. Even when seam flaws are generated, they are limited in the vicinities of the edges of the hot rolled steel sheet and moreover the seam flaws are not waved.