PURPOSE: To reduce the use amt. of a coating soln. without generating coating irregularity.

CONSTITUTION: A treatment chamber 5 is filled with a gas containing solvent vapor supplied from a solvent vapor supply source 12 through a diffusion passage 13. A substrate 1 is held to a horizontal posture in the treatment chamber 5 by a chuck 2. A nozzle 9 supplies a photoresist liquid to the center of rotation of the substrate 1 and the chuck 2 is rotated and the gas containing solvent vapor is sprayed on the peripheral part of the substrate from a vapor nozzle 17 along the rotary radius of the substrate 1. The photoresist soln. is spread over the surface of the substrate 1 by the centrifugal force by the rotation of the substrate 1 and spread over the surface of the substrate 1 by the pressure of the sprayed gas and spread over the entire surface of the substrate 1 rapidly and uniformly by the centrifugal force and the pressure of the gas. The treatment chamber 5 is filled with the gas containing the solvent vapor and the sprayed gas contains solvent vapor and the generation of coating irregularity is suppressed.