PURPOSE: To control accurately the sheet width of a hot rolling steel sheet, in a hot rolling equipment, by estimating the variation of sheet width at the outlet side of a downstream rolling mill by measuring continuously the sheet width at the outlet side of an upstream mill, and changing the flow rate of a rolling oil.

CONSTITUTION: In a hot rolling equipment provided with vertical mills 2, 2' and horizontal mills 4, 4' located at the upstream and downstream sides, the sheet width of a material 8 to be rolled is continuously measured at the outlet side of the upstream horizontal mill 4 by a sheet width detector 14. This signal is sent to an arithmetic device 16 to calculate the amount of sheet width variation in the longitudinal direction, and successively the amount of it at the outlet side of the downstream horizontal mill 4' is estimated by an arithmetic storage device 18 to calculate and store the changing amount of the flow rate of a rolling oil. When the material 8 is bitten by the downstream mill 4', a signal of the necessary changing amount of rolling-oil flow rate is sent by the unit 18 to a flow regulating valve controller 22, to change the oil flow rate by operating a flow regulating valve 24. In this way, the oil is sprayed on the material 8 from a spraying header 30 at a flow rate corresponding to the variation of sheet width.