A substrate treatment apparatus includes a substrate heating device for maintaining a substrate at a temperature higher than room temperature, a wetting device for producing a wet ozone-containing gas by wetting an ozone-containing gas with a treatment solution, and a supply device for supplying the wet ozone-containing gas from the wetting device to a work object on a surface of the substrate. The supply device includes a gas disperser including apertures aligned in rows in a width direction of the work object. The apertures in adjacent rows are not aligned with each other in a direction perpendicular to the rows. At least one of the gas disperser and the substrate is movable in a direction perpendicular to the rows. A gas conduit connects the wetting device to the supply device. A wet ozone-containing gas heating device heats the wet ozone-containing gas to a temperature at least equal to the temperature of the substrate.