PURPOSE: To execute square continuous rolling with a small-sized and inexpensive installation by specifying the sheet thickness between adjacent stands and the distance between the axial centers of rolls to specific conditions and reduction of area in plural alternate arrangements of horizontally driven and vertically non-driven rolling mills in which the first and final mills are horizontal rolling mills.

CONSTITUTION: A rolling material 20 enters first the horizontally driven rolling mill 1H and enters again the horizontally driven rolling mill 3H from the next vertically non-driven rolling mill 2V. The material is successively and repeatedly rolled by these mills and is discharged from the final horizontally driven rolling mill 2n+1H. The reduction of area of the vertically non-driven rolling mill is adjusted to ≥83% of the reduction of area of the horizontally driven rolling mill in this case. The relation of the thickness di of the rolling material 20 between the adjacent stands and the distance Li between the axial centers of the work rolls with the outside diameter Di of the work rolls is determined like the equations. The rolling material 20 forced into the vertically non-driven rolling mill 2V by the horizontally driven rolling mill 1H is passed through the mill without buckling and is pulled by the next horizontally driven rolling mill 3H by which the material is vertically rolled at ≥83% high reduction of area. The material 20 is thus smoothly rolled even if the vertical rolling mill is not driven and the square or nearly square continuous rolling is made possible.