To increase the variety of products, by setting a movable slitter and a pass line at the entrance of the finishing mill of a single strand bar rolling mill, by conducting slitting according to the products in need and by changing the pass line (finishing rolling block).

A slitter 16 movable to the side of non action position, and a pass line 18 are set to a main pass line P1 at the entrance of a finishing mill, together with the finishing blocks 42a and 42b, being set for bar materials changed from a main pass line P1 to P2 or P3. The auxiliary bars for construction use, the bars of small diameter or bars of lower quality are rolled after a slitting work of semi-rolled materials by a finishing block 42a or 42b respectively. The higher qualitied products are rolled either by the finishing block 42a or 42b without being slit, or when necessary, by a red roller block 66. Further, the bars of large diameter are transferred to a cooling bed 40 after an interim rolling.