PURPOSE: To heighten the accuracy of coating of a lubricant by making at least one of a doctor roll and a coating roll variable by a roll crown pressure regulating mechanism, and correcting the amount of roll crown basing on distribution of the thickness of oil film.

CONSTITUTION: A doctor roll 1 and a coating roll 2 are made to one set, and a nozzle 3 is placed between the two rolls. A solution of solid lubricant sent from a lubricant tank 4 is sprayed and coated on the surface and back of a steel plate uniformly. In this case, the coating roll 2 is formed to a variable crown roll structure and the distribution of the thickness of oil film in the direction of width of the surface of the steel plate after coating the lubricant is measured by an oil film measuring device 5. The crown of the coating roll 2 is regulated basing on the result of measurement. As the coating roll 2 uses an elastic material, pressure regulating sections 21a, 21b that act simultaneously over the whole circumferential direction are provided.