A method of treating an inorganic oxide film includes: dipping an inorganic oxide film having a plurality of pores therein which is formed by an oblique deposition method into a treatment liquid containing alcohol; reducing pressure of a space where the treatment liquid is provided to infiltrate the treatment liquid into the pores of the inorganic oxide film; and chemically bonding the alcohol to a surface of the inorganic oxide film and inner surfaces of the pores.