PURPOSE: To completely execute de-scaling of the rough bar on the hot rolling by controlling the dimension, the temperature of the material to be rolled after rough rolling and the height of high pressurizing water header for descaling.

CONSTITUTION: The temperature and the temperature change after rough rolling is controlled by controlling the dimension of the material 2 to be rolled after rough rolling, and the time for de-scaling is controlled by changing the temperature of the material 2 to be rolled after rough rolling e.g. with the heating device 4 or the cooling device and controlling the height of header of high pressurized water for descaling. Therefore, the scale of the material to be rolled can be removed completely while avoiding the temperature range of high scale detaching stress and executing the de-scaling effectively.