PURPOSE: To roll shape steels of low costs efficiently with low equipment costs by providing an open type caliber rolling mill group in succession to a high speed continuous casting machine on the line, and rolling the shape steels continuously without roll changing.

CONSTITUTION: A flat ingot of a small section is cast continuously at a high speed with a high speed continuous casting machine 3, and is fed with pinch rolls 6 to soaking pits 7, 7, where it is soaked. This is rolled by a breakdown mill 8 consisting of a vertical rolling mill 8a and a horizontal rolling mill 8b, then it is cut with a shear 9 to a rough steel ingot W1. The ingot W1 in the state of a hot ingot is loaded hot into a continuous heating furnace 12 via a loading hearth 11, after which it is formed with projecting parts on both sides in the central part thereof with a roughing mill 13. This ingot is subjected to the formation of an angle in the flange connection of an angle steel and to flange thickness and flange broadside rolling in double rolling mills 14, then to the formation of flange edges at the size of the flange width determined with universal rolling mills 15, whereby an intermediate formed material W2 is obtained. Finally, the material W2 is finished with a finishing mill 17, whereby the product angle steel W3 is obtained.