PURPOSE: To reduce the cost for production of 3-layered seamless clad steel pipes free from delamination by forming a tubular body having gaps and solidifying molten steel on the inside and outside of the formed body in a casting mold.

CONSTITUTION: A steel plate 2 or a steel wire 8 is formed spirally to a tubular body 4 having gaps 6. Or the plate 2 is formed to a tubular shape and is made into a tubular body 4 having a gap 6 in the longitudinal direction. The tubular formed body as an intermediate layer 4A is placed still and fixed in a casting mold by providing spaces for the inside layer and for the outside layer. Thereafter, molten steel to be cast into an outside layer 12 and an inside layer is charged simultaneously into the mold by top or bottom charging and is allowed to solidify. Or the body 4 as the layer 4A is inserted into the molten steel which is beforehand charged in the mold to solidify the steel. The steel ingot obtained in this case is not hollow but if a cylindrical core is installed therein, the hollow steel ingot consisting of 3 layers s obtained.