PURPOSE: To improve the yield of LSI or the like and to easily remove the residue of a coating agent, by preapplying a liquid having high viscosity and low vapor pressure to the inside of a cover of a rotary coater.

CONSTITUTION: A base plate 11 from a reservoir 10 is mounted on a vacuum chuck 13 by a mechanism 14, and a liquid, e.g. glycerol, having lower vapor pressure and higher viscosity than those of an As silica film liquid (an alcoholic of an As compd. and an organosilicon compd.) as a coating agent is dropped from a nozzle 16 and then scattered by the high speed rotation of the vacuum chuck 13 to form a film 18 on the side and the bottom surface of a cover 15. Thereafter, Si substrate 12 for diffusing impurities into them are successively mounted on the vacuum chuck 13, and the As silica film liquid is dropped from a nozzle 17 to perform rotary coating. When said rotary coating of the silica film liquid is performed on 15W25 pieces of predetermined substrate, a solid matter is gradually formed. Then, dropping of glycerol is performed again.