PURPOSE: To realize the manufacture of thin web H-beam in which a web wave is not generated, and also, toughness of a flange part is not deteriorated.

CONSTITUTION: On the delivery of a finishing rolling mill 6 of an H-beam steel rolling mill consisting of a rough rolling mill 4, an edging mill 5 and the finishing rolling mill 6, a forced cooling system 7 formed by arranging alternately plural strong water-cooling banks and weak water-cooling banks is provided, and forced cooling is executed to a flange so that a flange surface temperature enters within a temperature range of MS point to {MS+50°C}, and the system is controlled so that an average temperature difference between the flange and a web at the time when cooling is stopped becomes a prescribed value or below.