The present invention provides an oxynitride phosphor represented by a composition formula M(1)1−jM(2)jSibAlcOdNe (composition formula I) or a composition formula M(1)1−a−jM(2)jCeaSibAlcOdNe (composition formula II) and containing 50% or more of a JEM phase, and a light emitting device including a semiconductor light emitting element emitting an excited light, a first phosphor that is the oxynitride phosphor according to the present invention that absorbs the excited light and emits a fluorescence, and a kind or a plurality of kinds of second phosphor(s) that absorb(s) the excited light and emit(s) a fluorescence having a longer wavelength than the fluorescence emitted by the first phosphor. Thereby, a novel oxynitride phosphor being capable of highly efficiently emitting mainly a light having a wavelength of 510 nm or less and a light emitting device using the same can be provided.