PURPOSE: To produce easily a titanium slab having good quality at a low cost without requiring a rough forging stage by melting a square casting ingot of titanium which is tapered in the bottom and subjecting the molten titanium to blooming.

CONSTITUTION: A casting mold of a rectangular cross sectional shape which has the side walls curving outward and in which the adjacent side walls are continuous by having a radius is used in the stage of vacuum melting and casting of titanium by a vacuum arc melting method, etc. A casting titanium ingot having roughly a square shape is efficiently produced without distortion of the side walls of the mold. A mold of a desired shape is disposed in the bottom or the bottom and top part of the casting mold to taper the end part of the casting ingot. The workability in rolling is much improved by the above-mentioned method, by which the crop loss of the slab is decreased and the titanium slab is produced at a good yield.