PURPOSE: To improve the step coverage of a coating film and to uniformize the thickness of the coating film in this spin-coating method by spraying the solvent for a coating soln. into a chamber to suppress the vaporization of the solvent in the coating soln.

CONSTITUTION: A large-sized substrate 6 is fixed on a turntable 2 with a vacuum chuck. A coating soln. 7 with the viscosity specified is dripped on the substrate 6 from a pipe 3. At this time, the solvent for the soln. is sprayed into a chamber 4 from a spraying device 13 through a pipe 12 to practically saturate the chamber 4 with the solvent vapor. The solvent vapor pressure and its saturation degree are obtained by measuring the solvent gas concn. by a concn. measuring instrument 11 (e.g. gas chromatograph), measuring separately the pressure in the chamber 4 and calculating the measured values by a controller 14 (CPU). The calculated value and the set value are then compared, and the amt. of the solvent to be supplied from the device 13 is controlled to attain the set value.