A reflective mask blank that comprises a multilayer reflective film 13, protective film 14, and phase-shift film 16 for shifting a phase of the EUV light, which are formed in said order on a substrate 12. The protective film 14 is made of a material containing ruthenium as a main component, and an anti-diffusion layer 15 which is an oxidized layer containing ruthenium as a main component is formed on a surface of the protective film 14, or as a part of the protective film 14 on a side adjacent to the phase-shift layer 16, so as to inhibit counter diffusion in relation to the phase-shift film 16, thereby inhibiting the thermal diffusion between the protective film 14 and the material of the phase-shift film pattern. Also, a reflective mask and method of manufacture.