The present invention provides a blue phosphor that exhibits high luminance and shows less luminance degradation during driving of a light-emitting device. The present invention is a blue phosphor represented by the general formula aBaO.bSrO.(1−a−b)EuO.cMgO.dAlO3/2.eWO3, where 0.70≦a≦0.95, 0≦b≦0.15, 0.95≦c≦1.15, 9.00≦d≦11.00, 0.001≦e≦0.100, and a+b≦0.97 are satisfied. In this blue phosphor, two peaks whose tops are located in a range of diffraction angle 2θ=13.0 to 13.6 degrees are present in an X-ray diffraction pattern obtained by measurement on the blue phosphor using an X-ray with a wavelength of 0.774 Å.