Problem: There is a demand for a phase shift mask that makes it possible to decrease the film thickness of the phase shift film, can satisfy the requirement relating to pattern accuracy, without collapsing the OPC pattern, and enables control of optical characteristics and pattern defect inspection, and also for a phase shift mask blank as an original plate for such a phase shift mask.Means for Solving the Problems: A phase shift mask blank of the present invention has, on a transparent substrate, a phase shift film including, as main components, a metal, silicon (Si) and nitrogen (N), having optical characteristics of a transmittance of equal to or greater than 9% and equal to or less than 30% with respect to a wavelength of the ArF excimer laser beam and a phase difference of equal to or greater than 150° and less than 180°, and a light-shielding film formed on the phase shift film. A thickness of the phase shift film is equal to or less than 80 nm, and a refractive index (n) with respect to the wavelength of the ArF excimer laser beam is equal to or greater than 2.3, and an extinction coefficient (k) is equal to or greater than 0.28.