PURPOSE: To prevent the generation of surface flaw, to decrease the viscosity of lubricant and to reduce nozzle clogging by mixing solid lubricant with cooling water and spraying it on a rolled stock or places where are brought into contact with the rolled stock such as rolls, liners, etc., at the time of hot rolling.

CONSTITUTION: A solid lubricant which consists of iron oxide powder is introduced into a mixer 9 by taking compressed air or gas as a carrier and also mixed by introducing water or rolling oil. By spraying them from a jet nozzle 2 on the rolled stock 6 or the places where are brought into contact with the rolled stock such as the work rolls 1, liners, etc., the thinness of scale layer on the surface of hot rolled stock, especially, stainless steel is compensated. In this way, the generation of surface flaw due to burning is prevented by restraining metal-touch between mutual metals and, when the solid lubricant which is mixed with surfactant or thermoplastic matter is used, the diffusivity and transpotability of lubricant is improved and clogging in a pipe line is reduced.