PURPOSE: To prevent the development of oxygen segregation in a molten cast slab in the initial stage and to improve the yield by adjusting the oxygen content in the base material for melting at the initial stage of operation, at the time of executing continuous melting and casting by an induction melting method using a water-cooling type copper crucible.

CONSTITUTION: The oxygen content in the base material used in the initial stage of melting is made to be 50-90% of the oxygen content in the raw material successively charged in the melting of the base material, and the filling quantity into the crucible is made to be the quantity in the range shown in the inequality I. By this method, the increase of the oxygen quantity in the lower end part of the cast slab caused by absorption of the remained hydrogen in the chamber into molten titanium at the initial stage of the operation, is eliminated and a few oxygen segregations occur over the whole length and the cast slab having uniform quality can be obtd. Further, the yield of the cast slab is improved. Then, the reason why the filling quantity of the base material is regulated, is that in the case of too little, the dilution effect of the oxygen is not obtd. and reversely, in the case of too much, since the shortage of supplying of the oxygen into the molten base material is developed, the low oxygen part in the cast slab is formed.