A green fluorescent substance of the invention is higher in luminance of green than a conventional rare-earth activated sialon fluorescent substance and more excellent in durability than a conventional oxide fluorescent substance. The fluorescent substance is obtained by solid-dissolving Eu into a nitride or oxy-nitride crystal having a .beta.-type Si.sub.3N.sub.4 crystal structure, and emits a fluorescent light having a peak within a range of 500 nm to 600 nm in wavelength by being irradiated with an excitation source.
