A substrate treatment method of performing treatment on a substrate on which a pattern mask has been formed by exposure and developing treatment to improve roughness of the pattern mask includes the processes of: mounting and heating the substrate on a stage in a treatment container; then supplying a solvent gas to a center portion of a front surface of the substrate while exhausting the solvent gas from a periphery of the substrate to swell the pattern mask; and while performing the process of supplying and exhausting a solvent gas, forming a temperature gradient in the substrate via the stage such that a temperature at the center portion of the substrate is higher than a temperature at a peripheral portion of the substrate.