Steel is subjected to multiple-electrode submerged arc welding with three or more electrodes in which a direct-current power source is used to supply current to a first electrode, the welding by the first electrode is carried out at a current density of 250 A/mm2 or more, preferably with a wire diameter of 3.2 mm or less and a weld current of 1,000 A or more, the welding by the second electrode is carried out at a current density of 150 A/mm2 or more, preferably with a weld current of 600 A or more, one of the interelectrode spacings is 23 mm or more on a surface of the steel, and the remaining interelectrode spacings are 20 mm or less.