To obtain good material over the total length in a longitudinal direction of a steel sheet by joining the tail end of a preceding material and the front end of the following material on the entry side of a hot finish-rolling mill with a joining equipment and quenching the material near the exit side of the finish-rolling mill with a quenching equipment.

Between a rough-rolling mill 1 and a finish-rolling mill 3, the tail end of a preceding sheet bar (preceding rolled material) 18a and the front end of a following sheet bar (following rolled material) 18b are joined with a joining equipment 2. The rolled material is quenched with a quenching equipment 17 installed near the exit side of the final stand 3a of the finish-rolling mill 3. By joining, the preceding sheet bar (preceding rolled material) 18a and the following sheet bar (following rolled material) 18b are continuously finish- rolled, thus preventing occurrence of threading troubles of the front end of the following sheet bar (following rolled material) 18b. The quenching equipment 17 is installed within 5 m on the exist side of the final stand 3a, and it is desirable that it has the cooling capacity with heat transfer coefficient of 1,000 kcal/m2.hr°C or more.