PURPOSE: To reduce wear of a working roll and to prevent occurrence of roll slip in hot rolling of a strip by detecting surface condition of the working roll by plural detectors, and supplying rolling lubricant to the surface of the working roll according to the result of detection.

CONSTITUTION: Plural detectors 11 are faced to the surface of a working roll 1 for hot rolling of a strip in the direction of width, and quantity of rolling oil adhering on the surface of the working roll 1 is detected, and the signal is inputted to a controlling device 21. The controlling device 21 compares and calculates given input value and initial profile of the working roll 1 set beforehand, and outputs deviation value for each section of the surface of the working roll. This value is inputted to a control valve 19 and the quantity of injected oil from each nozzle 17 is controlled, and the quantity of adhering rolling oil over whole circumference of the working roll is made target value. Thus, wear of the working roll due to deficiency of rolling oil and slipping between the roll and strip due to excess of rolling oil can be prevented.