A fluorescent substance capable of remarkably increasing the luminous intensity of a I-III-VI2 chalcopyrite type compound having a large band gap among chalcopyrite type compounds with manganese as luminescence centers, and being favorably used for a lighting device using a light emitting diode, a light emitting element of a display device or the like, a light emitting device such as fluorescent lamps such as a cold cathode fluorescent lamp and a hot cathode fluorescent lamp, as a fluorescent substance generating fluorescence by ultraviolet excitation, is provided. The fluorescent substance is expressed by composition formula (1) Cu(Al1-xGax)(S1-ySey)2:Mn,Si  (1) (wherein x represents a number satisfying 0≦x≦0.4, and y represents a number satisfying 0≦y≦0.4), including manganese as a luminescence center atom.