A method for processing a substrate with a porous film having a porous structure formed on a surface layer thereof includes the following a) and b) steps. The a) step is a step of mixing a first processing solution containing water with gas to generate droplets of the first processing solution and injecting the droplets of the first processing solution to the porous film. In addition, the b) step is a step of, after the a) step, mixing a second processing solution which is an organic solvent having higher volatility than the first processing solution with the gas to generate droplets of the second processing solution and injecting the droplets of the second processing solution to the porous film.