Provided are a reflective mask blank and a reflective mask that can improve the contrast for EUV exposure light in use of the mask and further can improve the pattern resolution at a pattern edge portion of the mask, thereby enabling high-resolution pattern transfer. A reflective mask blank of this invention has a substrate and, further, a multilayer reflective film adapted to reflect the EUV exposure light and an absorber film adapted to absorb the EUV exposure light, which are formed in this order over the substrate. The absorber film is made of a material containing Ta and has a film density of 6.0 to 16.0 g/cm3. A reflective mask is obtained by forming a transfer pattern in the absorber film of the reflective mask blank.