To prevent foreign matters from adhering to a substrate, etc., thereby causing inconveniences during storing and transporting a mask blank, or during manufacturing the mask blank and a mask. Thin films 2 and 3 formed in a mask thin film forming step of a mask blank manufacturing steps are covered by a dust-free protective film 5 formed of water-soluble material, thereby preventing foreign matters from adhering to the surface of the mask blank itself and preventing the surface of the mask blank from being damaged in the subsequent step, and when the mask blank is used, the dust-free protective film is removed.