Provided are a reflective mask blank and a reflective mask that are capable of reducing the shadowing effect of EUV lithography and forming a fine pattern. As a result, a semiconductor device can be stably manufactured with high transfer accuracy. The reflective mask blank has a multilayer reflective film and a phase shift film that causes a shift in the phase of EUV light on a substrate in that order, wherein the phase shift film comprises a single layer film or multilayer film of two or more layers and is made of a material comprising tantalum (Ta) and titanium (Ti).