PROBLEM TO BE SOLVED: To provide a thick board rolling method by which the productivity of a thick board product can be improved.SOLUTION: In a case where the length of the material of a roll material S is equal to or greater than the value in which a marginal length is added to the required length of a thick board product, and in a case where the product of the thickness and width of the roll material S is divided by the required thickness of the thick board product is equal to or greater than the value in which a marginal width is added to the width of the product, it is detected that the thick board product can be obtained by subjecting the roll material S to only broadening roll. The roll material S is subjected to only broadening roll, as a rolling step. Therefore, the thick board material S to be subjected only broadening roll may be a thick board material S in which only the thickness in broadening roll is added. Thus, thick board material S is reduced by an ingot casting method is reduced, and thick b
