To provide a phase-shift mask in which the reduction in thickness of a light-shielding film is provided when a transition metal silicide-based material is used for the light-shielding film and by which the problem of ArF light fastness can be solved; and a mask blank for manufacturing the phase-shift mask.A mask blank 10 comprises a phase-shift film 2 and a light-shielding film 4 on a transparent substrate 1, the phase-shift film 2 is made of a material with ArF light fastness, and at least one layer in the light-shielding film 4 is made of a material which contains transition metal, silicon, and nitrogen, and satisfies the conditions of Formula (1) below: CN≤9.0×10−6×RM4−1.65×10−4×RM3−7.718×10−2×RM2+3.611×RM−21.084  Formula (1) wherein RM is a ratio of the content of transition metal to the total content of transition metal and silicon in said one layer, and CN is the content of nitrogen in said one layer.