A fluorescent substance is provided having excellent temperature properties and capable of being excited by light in the region from near ultraviolet to short-wavelength visible light to emit light of yellow to red color. A process for producing the fluorescent substance, and a light emitting device using the fluorescent substance is also provided. The fluorescent substance includes M which is at least one group II element selected from Ca, Sr, and Ba, and Al, Si, O, and N, and activated with Eu. The fluorescent substance has an X-ray diffraction pattern using CuKα radiation, in which the intensity of the diffraction peak in the Bragg angle range of 17.9° to 18.5° is taken as 100%, the relative intensity of the diffraction peak is 150% to 310% in a Bragg angle range of 24.5° to 25.1° , and is 320% to 550% in a Bragg angle range of 34.8° to 35.4°.