PURPOSE: To preform the front and rear ends of a steel material without the need for stopping or positioning the steel material by using a cam rolls on the inlet side of a rolling mill in place of dies for rolling down said ends in the transverse direction.

CONSTITUTION: A pair of freely rotatable eccentric (or elliptical) cam rolls 5 are provided on the inlet side of a cross rolling mill 4. The rolls 5 have a circular cross section and eccentric revolving shafts. The gap between the roll is adjusted by the rotation of a screw shaft 6. Cylinders 7 for starting the rolls 5 and hardware 8 are provided in the upper part of the rolls 5. When a steel material 1 is transferred, the gap of the rolls 5 is narrowed, and the cylinders 7 press the hardware 8 to apply rotating force on the rolls 5; thereafter, the rolls 5 are rotated by the frictional force of the steel material, whereby the steel material is preformed. A computer controller 9 is inputted with the width and length of the steel material from an upper program controller 10 and the time for passage of the front end of the steel material from a sensor 11 and performs automatically the above-mentioned operation when the preforming position at the front end of the steel material arrives at the rolls 5 from the rotating speed of table rolls 12.