A method which can perform a soft pre-wetting treatment of a substrate, such as a wafer, with use of a pre-wetting liquid in a smaller amount. This method includes: holding a substrate between a first holding member and a second holding member, with the surface of the substrate being exposed through an opening of the second holding member, and pressing a sealing ridge of the substrate holder against a peripheral portion of the substrate; pressing a sealing block against the substrate holder; forming a vacuum in an external space; performing a seal inspection to check a sealed state provided by the sealing ridge based on a change in pressure in the external space; and performing a pre-wetting treatment by supplying a pre-wetting liquid to the external space while evacuating air from the external space to bring the pre-wetting liquid into contact with the exposed surface of the substrate.