Disclosed is a reflective mask blank (10) which comprises a substrate (1), a multilayer reflective film (2) for reflecting exposure light, a buffer film (3), and an absorber film (4) for absorbing exposure light, said films being sequentially formed on the substrate. The absorber film (4) has a multilayer structure which is composed of an uppermost layer (4b) and a lower layer (4a). The uppermost layer is formed from a material containing oxide, oxynitride or carbide of Ta, and has a refractive index (n) of 0.95-0.97 and an extinction coefficient (k) of from −0.033 to −0.023. The lower layer is formed from a material containing Ta, and has a refractive index (n) of 0.94-0.97 and an extinction coefficient (k) of from −0.050 to −0.036. A reflective mask (20) can be obtained by forming a transfer pattern on the absorber film of the reflective mask blank.