A method of manufacturing a mask blank includes a thin film forming step of forming a thin film, which becomes a mask pattern, on a mask blank substrate and a resist film forming step of forming a resist film on the thin film. The method further includes a step of storing resist film forming information including information about a date of formation of the resist film on the thin film, a step of correlating the resist film forming information with the mask blank, a step of identifying, based on the resist film forming information, the mask blank having the resist film whose sensitivity change exceeds an allowable range, a step of stripping the resist film formed in the identified mask blank, and a step of forming again a resist film on the thin film stripped of the resist film.