To facilitate a fining and a uniformizing of structure in an inner part of a steel ingot and to obtain a steel ingot excellent in toughness by directly vibrating a non-solidified part in the steel ingot containing specific wt.% of elements with a rod or indirectly vibrating a molten metal through an ingot case and executing a specific heat treatment after completing solidification.

Just after completing the casting of the steel ingot containing by wt.% of e.g. 1.8% C, 0.5% Si, 0.6% Mn, 0.02% P, 0.005% S, 1.1% Cr, 0.5% Mo, 0.01% V and the balance Fe with inevitable impurities, the tip part of the mild steel-made rod 4 having 100mm diameter and 1000mm length is dipped to the position having 300mm depth from a feeder head surface. The rod 4 is vibrated by working a vibrating motor 5 and the molten metal whose solidification progresses from the outer periphery of the steel ingot to the inside, is succeedingly vibrated for 2hr after casting with the rod 4. The rod 4 is cast as it is into the feeder head. The steel ingot completing the solidification is cooled in the furnace at cooling speed of ≤20°C/h after holding at 870°C for 10hr.