PURPOSE: To suppress the generation of wire-shaped flaws at the ends of a slab and to remarkably improve the yield by preliminarily subjecting the ends of the slab to edging rolling by using caliber rolls having the prescribed shape specified with a groove width and the angle of inclination of groove side faces.

CONSTITUTION: The slab 1 is preliminarily subjected to edging rolling by using the caliber rolls 2 at the time of subjecting the slab to horizontal rolling. Each of the caliber rolls 2 is formed of a groove base 2a having a circular columnar side face shape and a conical surface-shaped groove side face 2b having the prescribed angle θ of inclination. The width (b) of the groove is sized smaller by 20W40mm than the thickness of the slab and the angle θ of inclination is specified to 25W35°. The ruggedness and wrinkles of the slab side faces are eliminated by rolling down the ends with such caliber rolls 2. The generation of the wire-shaped flaws at the transverse ends on the front and rear of a thick steel plate is thus suppressed and the yield of the product is remarkably improved.