Disclosed is a blue light-emitting phosphor powder which has more excellent emission characteristics than the conventional rare earth element-activated sialon phosphors and more excellent durability than the conventional oxide phosphors. The solving means resides in: firing a starting material mixture in a nitrogen atmosphere at a temperature range between 1,500 DEG C inclusive and 2,200 DEG C inclusive, wherein the starting material mixture is a mixture of metallic compounds, and is capable of constituting a composition comprising M, A, Si, Al, O, and N (M is one kind or two or more kinds ofelement(s) selected from Mn, Ce, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb; and A is one kind or two or more kinds of element(s) selected from C, Si, Ge, Sn, B, Ga, In, Mg, Ca, Sr, Ba, Sc, Y, La, Gd, Lu, Ti, Zr, Hf, Ta, and W) by firing; to obtain a phosphor which emits fluorescence having a peak at a wavelength within a range of 400nm to 700nm, by irradiation of an excitation source.