Abstract: A method of producing a mold steel, the method including a first process of preparing a molten steel A that is obtained after vacuum refining and has a component composition including from 0.005% to 0.1% by mass of C, from 1.0% to 5.0% by mass of Ni, from 3.0% to 8.0% by mass of Cr, more than 0% but less than or equal to 2.0% by mass of Mo, more than 0% but less than or equal to 3.5% by mass of Cu, and more than 0% but less than or equal to 2.0% by mass of Al, in which an amount of O is 0.005% by mass or less and an amount of N is 0.03% by mass or less; a second process of reducing the amount of O and the amount of N in the molten steel A, by slag refining the molten steel A, to obtain a molten steel B; and a third process of casting the molten steel B, is provided.